My sister took possession of the family home which upon her selling it, the profit would be split three ways.
What does this mean? Who inherited the property?
My sister just sold it. We each received $96,000. It was GIFTED from my oldest sister since through a mortgage, had it in her name, not a trust.
That might have been the way you handled it informally, but I don't think that is what happened.
I was going to start doing an if/then, but I'll decline until an answer comes for the first question. How was it inherited?
I bet you set up an informal trust for the house and each owned 1/3 of it. I'm not sure the sister who lived there "owned" the property under the grantor trust rules in this type of situation because each granted property to the trust and no one could change or amend the agreement. I'm not absolutely certain of that and would have to go over the facts carefully to be sure. But, at best, only the sister who lived there would get the section 121 exclusion talked about by efflandt above and I don't think any would.
Now, the sisters may get away with the "gifting" scenario the OP is trying to push. If sister who lived there took the property into her own name directly from the estate, who's to say the other sisters didn't disclaim their rights to the house? As long as there was no agreement to later split the profits, the sister can now gift over portions to the other sisters. We have the problem of the agreement which would make this tax fraud, but a hard fraud to prove. (Depending on the specific facts.)
See a tax professional this year. You don't get to do things informally and without documentation and later decide to make up facts which work out easiest and best. I think all three inherited. A trust was created with the agreement to split the profit three ways. (Don't even get me started on this informal trust which is not in writing which of and concerns land.) I think this is a simple capital gains question. No matter the choice made it will probably be OK. But, if it goes bad for some reason, this could go very bad with lots of lawyers fees and penalties.
See the guy this year. Let him advise you after looking at the facts.