The best approach may be to use "substance over form."  Did the parents really intend for the kids to have a marketable interest in the property?  Did the kids even know they were given a remainder?  Or should the sale be reported 100% on the mother's return -- presumably she qualifies for the $250K exclusion?

But were multiple 1099-S's issued to all five parties?  Who get the money?  If the kids got a check, did they turn the money over to their mother, or is this part of a scheme where the kids get cash to go on a cruise and Mom gets to stay at the county home at taxpayer expense?  

And whose return are you doing -- Mom's?  A kid?  Some or all of the others?  

If the family weren't allergic to professional advice, they could have avoided the problem by deeding the remainder interests back to Mom before the house was sold.