Capital Gains impact of Selling part ownership: Tenants-in-common

[Tenant-in-common]

My two brothers and I own a rental condo.  They decided to do an AirBNB and I refused.  I asked for them to buy me out.  We hired a lawyer to do the transaction.  They paid me the portion I would have paid for the outstanding mortgage on the condo which is lower than 1/3 fair market value of condo.  So filing 2021 taxes and filling out Capital Gains schedule.....is the proceeds what they paid me, or do I estimate a fair market value of the condo?  In addition to the lawyer fees, can I also add an assumed real estate commission (ie. 5% of proceeds) as part of the outlay expenses?  Need confirmation of this one as I saw some reddit forums say they could.