If my brother has lived with a women for 30 years but they never married, if she is in the hospital what are his visitation rights?

Your brother, unfortunately--and he has our sympathy--may have relatively few rights. An unmarried significant other has no legal rights to property and/or to visitation or over medical treatment. There would have been ways around this, had they been done previously--for example, living wills, medical or more general powers of attorney, a will to make sure that he, if the worst happens inherits, etc. Without those things, your brother has essentially the same rights as a tenant in her home would have, via-a-vis property and residency:

1) He can't be evicted or locked out without an eviction proceeding being brought against him by someone who owns the home. And if the son does not have guardianship or a POA over his mother, then he would not have the standing to do this--though if he does have a guardianship or POA, the son may have the authority to evict your brother.

1a) Note that even if the son can evict your brother, he can't just lock him out--that's illegal. He has to do it through the courts. So you brother may have a cause of action for illegal eviction.

2) Also, even if properly evicted, your brother can't be kept from his own property.

2a) An issue though may be proving it's his own belongings, and not hers, if the belongings are in her home and could belong to her; e.g. ownership of a TV is debatable, but he can show that the men's clothing is his.

2b) Items bought jointly--like a hypothetical TV--are things where your brother may be able to show some interest in, based on how much he can prove he paid, and therefore be entitled to a portion of them or their proceeds.

3) The son can keep him out of the hospital; the son is presumably the next of kin.

4) If there's no will naming your brother, the son will presumably inherit if his mother dies.

Your brother should consult with an attorney about the specifics of his situation. He needs to be prepared that he may have relatively few rights, other than to reside in the house until someone with authority can evict him legally, and to take those belongings he can prove are his if and when he leaves.