My Sister-in-law and brother-in-law been together for over 45 years and have 6 children all Adult's now. My brother-in-law is in a care home who suffers from senial Dementia. They both want to get married so how do they go about this and is there any law that say's they can not marry.
Would your brother-in-law be considered competent to enter into a contract or to make legal and medical decisions for himself? I don't think that anyone could argue that SIL is a gold-digger coming in to take advantage of the man! But I don't know what the rules might be concerning competency. I'll bet that a call to the Senior Helpline in your area could answer that.
Is there anybody at all who would be likely to get their undies in a bundle and contest this marriage? If there are no disgruntled relatives on either side, I'd say start buying confetti and offer to take SIL out to buy a nice dress for the occassion!