
<PAGE>
 
    Exhibit (c)(9)


                               FIRST AMENDMENT TO
                        AGREEMENT AND IRREVOCABLE PROXY


              THIS FIRST AMENDMENT TO AGREEMENT AND IRREVOCABLE PROXY (this
    "Amendment") dated as of March 21, 1996 by and among MARRIOTT INTERNATIONAL,
    INC., a Delaware corporation ("Parent"), FG ACQUISITION CORP., an Indiana
    corporation and a subsidiary of Parent ("Purchaser"), APOLLO FG PARTNERS,
    L.P., a Delaware limited partnership ("Shareholder"), and FORUM GROUP, INC.,
    an Indiana corporation (the "Company"), amends the Agreement and Irrevocable
    Proxy dated as of February 15, 1996 (the "Original Agreement"; the Original
    Agreement, as amended by this Amendment, the "Agreement") by and among
    Parent, Purchaser, Shareholder and the Company.


                              W I T N E S S E T H:
                              ------------------- 

              WHEREAS, pursuant to the Original Agreement, Shareholder agreed to
    exercise the Citicorp Warrants (as defined in the Original Agreement) it
    holds and to tender the Citicorp Warrant Shares (as defined in the Original
    Agreement) acquired upon such exercise into the Offer (as defined in the
    Original Agreement); and

              WHEREAS, Shareholder now wishes to sell the Citicorp Warrants to
    Purchaser and Purchaser is willing to buy the Citicorp Warrants for an
    aggregate purchase price of $3,455,557.23 (the "Citicorp Warrant Purchase
    Price"), which is equal to the difference between the aggregate price that
    would have been paid for the Citicorp Warrant Shares pursuant to the Offer
    and the aggregate exercise price of such Citicorp Warrants.

              NOW, THEREFORE, in consideration of the foregoing and the mutual
    premises, covenants and agreements contained herein, the parties hereto,
    intending to be legally bound hereby, agree as follows:

              1.   Capitalized terms used and not defined herein have the
    respective meanings ascribed to them in the Original Agreement.

              2.   Section 2(b) of the Original Agreement is hereby deleted in
    its entirety and replaced with the following paragraphs:

              "(b)  (i)  Prior to the expiration of the Offer, Shareholder shall
         deliver the Citicorp Warrants to Purchaser pending the acquisition of
         such Citicorp Warrants by Purchaser for the Citicorp Warrant Purchase
         Price, as set forth in clause (ii) of this Section 2(b).

                    "(ii)  Promptly after First Chicago Trust Company of New
         York, as Depositary for the Offer, has issued payment in exchange for
         all of the Company
<PAGE>
 
         Common Stock tendered in the Offer, Purchaser shall acquire the
         Citicorp Warrants by paying the Citicorp Warrant Purchase Price to
         Shareholder by wire transfer, provided that instructions for such wire
                                       --------                                
         transfer shall have been delivered by Shareholder to Purchaser."

              3.   Section 2(c) of the Original Agreement is hereby deleted in
    its entirety and replaced with the following paragraph:

              "(c) Prior to the expiration of the Offer, Shareholder shall
    deliver the Investor Warrants to Purchaser to be held in escrow pending the
    consummation of the Offer. The Company and Shareholder agree that,
    notwithstanding any provision of the Investor Warrants or the Acquisition
    Agreement to the contrary, upon expiration of the Offer and without any
    further action whatsoever, the Investor Warrants held by Shareholder shall
    be deemed cancelled and extinguished, for no additional consideration
    whatsoever. The Company shall mark the Investor Warrants cancelled upon
    receipt thereof. Prior to the expiration of the Offer, Shareholder will
    neither transfer nor exercise any Investor Warrants for any reason
    whatsoever."

              4.   The following paragraph shall be added as Section 2(e) of the
    Agreement:

              "(e)  Upon payment of the Citicorp Warrant Purchase Price pursuant
    to Section 2(b)(ii), the Company shall cause the transfer of the Citicorp
    Warrants from Shareholder to Purchaser to be recorded on the record books of
    the Company."

              5.   Miscellaneous.
                   ------------- 

              (a) The Agreement, as amended hereby, constitutes the entire
    agreement among the parties with respect to the subject matter hereof and
    supersedes all other prior agreements and understandings, both written and
    oral, among the parties with respect to the subject matter hereof.

              (b) All costs and expenses incurred in connection with this
    Amendment and the transactions contemplated hereby shall be paid by the
    party incurring such expenses, and each of Parent and Purchaser, on the one
    hand, and Shareholder, on the other hand, shall indemnify and hold the other
    harmless from and against any and all claims, liabilities or obligations
    with respect to any brokerage fees, commissions or finders' fees asserted by
    any person on the basis of any act or statement alleged to have been made by
    such party or its Affiliates.

              (c) This Amendment shall be governed and construed in accordance
    with the Laws of the State of Delaware (regardless of the Laws that might
    otherwise govern under applicable principles of conflict of laws) as to all
    matters, including matters of validity, construction, effect, performance
    and remedies.

              (d) The descriptive headings used herein are inserted for
    convenience of reference only and are not intended to be part of or to
    affect the meaning or interpretation of this Amendment.
<PAGE>
 
              (e) This Amendment may be executed in counterparts, each of which
    shall be deemed to be an original, but all of which, taken together, shall
    constitute one and the same instrument.
<PAGE>
 
              IN WITNESS WHEREOF, Parent, Purchaser, Shareholder and the Company
    have caused this Agreement to be duly executed as of the day and year first
    above written.

                                  MARRIOTT INTERNATIONAL, INC.


                                  By:  /s/ Joseph Ryan
                                     ------------------------------------
                                       Name:  Joseph Ryan
                                       Title: Executive Vice President


                                  FG ACQUISITION CORP.


                                  By:  /s/ Edward L. Bednarz
                                     ------------------------------------
                                       Name:  Edward L. Bednarz
                                       Title: Vice President


                                  APOLLO FG PARTNERS, L.P.

                                  By:  Apollo Advisors, L.P.,
                                       Its Managing General Partner

                                        By:   Apollo Capital Management, Inc.,
                                         Its General Partner

                                        By:  /s/ Michael Weiner
                                           -------------------------------
                                           Name:  Michael Weiner
                                           Title: Vice President


                                  FORUM GROUP, INC.


                                  By:  /s/ Mark Pacala
                                     ------------------------------------
                                  Name:   Mark Pacala
                                  Title:  Chairman and Chief Executive Officer
