Who Makes The Decisions In Absense Of A Living Will?

I'm sure this is a state by state mandate. (I live in Indiana btw)
But my brother is in the hospital and unable to respond.
He has a living mother and 2 adult sons.(and a wicked girlfriend)
I think the g/f has implied to the staff that they are married and keeping certain family members out.
I know that SHE HAS NO RIGHTS.
But to set the record straight, who would have rights by default, his mother or his sons.
If you don't know, don't guess. Thanks!

In your case, you and your mother will need to speak to a patient's advocate, or similar position at teh hospital. Explain that the g/f has no rights and that you will sue the hospital if they continue to entertain her as they have been. You can even bar her from visiting your brother. If they start a fuss, simply state that unless she (the g/f) provides proof that they are married, then you will file suit immediately. DON'T WORRY, the hospital will side with you as they experience this often. The first mention of a lawsuit will be an extra incentive for them to comply with the law.

In almost all jurisdictions, it will be the Next of Kin.
This is determined in progression:
1) Spouse (if any)
2) Children (if any)
3) Parents (if any)
4) Siblings (if any)

His Son's are his heirs, but without a living will or trust everything will go to probate. Nobody has rights to speak on his behalf without a POA. The hospital may ask the Sons, but they don't have to. I'd set the hospital straight on the GF before they start asking her over the Son's what should be done, if they do ask. So sorry to hear about your brother, my best wishes to your family.

His mother. Make her prove that they are married - if it's true, she will be the legal representative.

If his mother doesn't want to do it, it would fall to his sons - a girlfriend is not even in the line.

Next of kin. Since the children are adults, they are next of kin, then the mother. He MIGHT have signed a power of attorney to the girlfriend.

Most places

Mom
the sons.