Can my siblings leave me (oldest daughter) out of medical decisions? Is this legal? What do I do?

Was the feud over mom's care? Are you the caregiver? Tread carefully if you are not the caregiver.

Are you forbidden to contact your mother? Unless you are, why not visit her and see for yourself how she is getting along?

Does someone have healthcare power of attorney? POA?

Generally a facility wants to deal with one family member. In our family that is me. (Mother never named POAs.) The NH notifies me of meetings. I notify the siblings I choose to notify. Among us we make sure at least one of us will be there. I discuss all decisions with the sibs who are interested, although I have no legal requirement to do so.

I take it that somehow one of your siblings is the contact person for your mother. If that is not backed up with a legal authority (POA) then you can probably call the nursing home directly and ask when the next care conference is, and attend those.

The absolutely best outcome would be to end the feud. Working together for Mom's benefit is the mature approach, even if you are no longer social friends.

Build bridges, mend fences and support their decisions. Nobody likes making the difficult decisions, sometimes what mom wants is not what is the safest option for her. Our mom wants to go home. She has tried to get the kids arguing among themselves, to divide them and get her way. She plays the guilt card, the money card, the health angle, tries to stir up distant relatives with tales of neglect, none of it has worked. You may be a victim of similar rants. We saw her coming, we all got on the same page. Get on the same page.

The person holding the healthcare power of attorney has ultimate control over healthcare decisions for your mom if she is incapable of making them for herself. Not particularly nice, but legal. Your only option would be some kind of court action. Talk to an elder care attorney to see what you might be able to do.