@Merc450
Sorry to hear your Mother is in a home - but if your mother's grandson has occupied the house for 10 years - there are at least three concerns:
1. Promissory Estoppel - was the grandson induced to stay in the house for the purposes of keeping your mother company or secure? What I am getting is that he may have been promised some benefit other than the rent free occupation..
2. Adverse Possession - if he occupies the house for 12 years without any objection from the owner .. so what does the 10 year occupation involve - was there an implied licence (as in permission) which would defeat adverse possession
3. The will - should decide it unless he is the child of a deceased child in which case he may have right to inherit a proportion of house.
You probably need legal advice.