Wait. The house is most likely NOT the inheritance of the CHILD who was under 8 at the time. Most married people hold a house as joint tenants with right of survivorship. The kids don’t get the house if one parent dies or if there is a divorce. If there was no will, state law will apply but rarely would the children get a property titled to the parents, or get a big part of the property.
The OP didn’t say everything each of them had when they married 10 years ago they kept separate, just that the amount they’d saved for college up to that point went to the children of that parent. Since then, they have been saving for college at the same rate for all 4 kids.
If the husband had held on to the second house, the OP’s triplets would have been penalized in the FAFSA/CSS filing (second house owned by stepfather) so how would it be immoral for them to want to benefit from the sale? Wouldn’t it have been ‘immoral’ for the stepfather to retain assets that hurt the triplets, an asset that they had no claim to?
If the stepchild has assets of her own, SSI payments from her mother, gifts from maternal family, sure, those are hers. A house? No, not hers.