Sibling Inheritance Forced buyout - capital gains?

What, exactly, are you trying to accomplish?

The property should most likely have received a stepped-up basis upon the death of the grantor.

Actually, you probably need to provide more details on the transaction and circumstances.

as @tagteam mentioned we need more info to be sure but most likely the property received a stepped-up basis upon the death of the owner. Now the property with the stepped-up basis is being sold. thus, it would seem any gain would be the difference between the sales price and stepped-up basis.

If the taxpayer owns property, and sells it, their gain is the difference between their basis and the selling price.  If the property does not get a stepped up basis (which may be the case for certain trusts), then the buyout is a taxable capital gain.  It doesn't matter than the sale was forced.  

However, most inherited property should get a stepped up basis.  The taxpayer should have an attorney at this point, and if the attorney doesn't specialize in the tax issues of the transaction, the taxpayer should also hire an accountant to advise on the gains issue.  

The trustee distributing the property (i.e., transferring it to the beneficiaries via deed) should know the basis of the property.

The issue, I believe, that @LeroyButch is addressing is whether the sale (via partition suit) or settlement (via buyout) can somehow be treated as a cash inheritance (e.g., no income tax liability) or otherwise. Clearly, the transaction here must be treated as the sale of a capital asset and not a cash inheritance with the beneficiaries taking the trust's basis in the property distributed.

Agreed, the taxpayer is selling property, and that's a capital gains transaction.  The basis of the property may be affected by various factors.  But the fact that the sale is forced, rather than voluntary, does not allow the taxpayer to treat the proceeds as a non-taxable cash inheritance.