Shared right to occupy

H and W and 3 children, son lives at home with the parents. House in sole name of W, ultimately will go to the 3 children equally. She wishes to protect the husband and the son so they are not forced to leave the property. W not happy with a right to occupy/life interest for H (even with condition for son to live there) as she feels when that interest determines the son may be forced out by the other 2 siblings wishing to cash in their interests. She wishes to give them a shared right to occupy. I can see many issues with this e.g. she is happy for the son to cohabit/marry and still retain the right, but not the H. I was thinking a right to occupy for the son with a condition on the H being able to reside there etc, then if the son’s interest determines (e.g. he moves out) then a right to occupy then arises in favour of H. I realise there are IHT implications here but the estate is not large and H does not own anything as such. Any thoughts would be appreciated.