Tiger, I'm curious,
How is this affecting the childrens relationship with both father and grandparents? I can't imagine that the relationship (if their Grandma and Grandpa have served you with an eviction notice, want you to leave the house that is rightfuly theirs on the deeds, that you have lived in rent free for 15 yrs, in which a bit of money for maintenance has been spent, that you now say should be yours) is going too well?
Would it not be better for their sakes to count your blessings so far and start afresh?