My formerly estranged brother has transitioned and wants back in mine and my mother’s lives.

What was he like previously- does he like drama? Is he wheedling his way back in because he’s bored and likes creating upset?
Is it attention? He likes the attention and wants to come back as this ‘I was a shit because I was unhappy and poor me.’
Could it be inheritance? Now your dad has passed and he wants to make sure he is still in the will.

I don't share your views, but I still wouldn't be thrilled that an estranged sibling just felt like they could decide they wanted to rekindle and expect me to agree. I think my feelings would be the same regardless of transition
"I am an adult and perfectly able to be civil when we cross paths, but I'm not interested in developing a relationship beyond that."

This sounds dreadful. Maybe you can be the side your mum can’t express. See him but just treat him as you’ve always known him.
With narcissists in my family I keep organised focus on other people and topics (planning events or visits to coincide with their visit) so they any take too much attention.

Male or female he’s still an arse.

Annoying he’s doing it near Christmas. He sounds very attention-seeking. Chickens always come home to roost and I doubt his relationship will be very healthy either.

If you can maintain a bit of emotional distance (with occasional venting to trusted people!) and stay rooted in your own life and family, it might just be interesting.

Is he back because he thinks there is money following your Dad's death? If, as you say he is nasty then he may be sniffing around your Mum while she is grieving with the intention of getting what he can out of the situation

I'd expect him to start pressuring your mother to get you on board, so in your shoes I'd be thinking hard about what boundaries you want to set. Then tell your mum what they are; and think hard about how you handle it when he starts bullying her to lean on you to breach them.

I hope your mum is grounded!

Even before this, he was nasty enough for you to want nowt to do with him. Keep him well away from your kids at the very least - he'll send them trans kiddie books just to spite you.

I don't have experience with an estranged brother coming out as trans. But I do have experience with relatives who have lost a spouse quickly thereafter being pressurised into a relationship with an estranged child. And it's not gone well. In each case the child has been a real drain on their parent, none of them have given more they've taken. It's been heartbreaking to watch.

I don't know what would work best for your mum, but I would remind her that she's in the throes of grief, and that she doesn't have to move at your brothers pace. If you feel up to it, you could offer to run interference with some of the relatives who your brother has tried to get on side. Reminding them that your mum has just lost her husband and your brother doesn't seem to have changed his spots even if he's changed his dress.

Agree with others that from your perspective, holding the line that you are happy with the estrangement and don't want a relationship with him seems better than addressing his transition and your GC views with him.

If you were trundling along ok in the status quo when you were estranged there's no need for you to be back in contact now. If your Mum wants a relationship with him she needs to see it as separate to YOUR relationship with him. You can say to her that he may want to reconnect - but you are quite happy to carry on as you were. And neither of them get to make that decision for you.

OP, he has been horrible innthe past.
You do not have to move on or have anything but the most surface of interactions if you do meet among wider family.
You do not have to see him at your mothers home.
You do not have to receive him in your home.
You certainly do not have to allow him near your children.

Tell your mother you support and respect her choices, but the staus quo suits you.

Just because he wants to have a relationship with you again, doesn't mean he gets to.

You 100% have agency.
I wouldn't mention his transitioning at all.
Nothing to do with you, you are not in contact.

Canvasing wider family before your mother is highly manipulative.

I would hold strong and be calm and clear with your mother that for you, things remain as is.

If your mother attempts to put pressure on you, she is no better than him.

If you wish for an excuse, you could say you will NEVER get over his treatment of your father, and have no wish to be in contact going forward.
He cannot argue with that.

He might think he'd 'like' a relationship with you - he can like what he wants, that doesn't entitle him to one.

This sounds a bit like 'whole new me' aimed to erase all previous history, or an expectation that transition opens previously closed doors and requires indulgence or sympathy. It in fact doesn't change the history at all, or him as a person, or your feelings in any way. If you didn't want contact before, why would him transitioning change that situation for you? You're not obliged to do or feel anything different OP, the history and your judgment to this point remains unchanged.

If it's a case of approaching you with a sincere attempt to mend fences then it doesn't matter what his pronouns currently are or how he's presenting, it's how you would feel about exploring that, and how sincere he turns out to be. If you then find it goes well and you want to mend those fences, that's lovely. But I would unfortunately be wary of whether this was being invited into new games as it can be, or whether refusal to do what he wants now has a new way to deal with it, by calling it 'transphobia'.

Even if it all went well I would also be very wary of bringing children into all this, with all the history involved, until I'd myself done a lot of building the relationship back up, until I was certain it was going well, and that it offered the children long term stability in the relationship, and I felt in a certain enough place to think about re introductions. If he's actually serious about caring about you and the children then he'll understand this, support you and be keen to put the time into building up trust. If he wants to rush to contact with a lot of guilt involved? You've got your answer.

There are at least two posts on this thread telling the OP how to deal with her sister. I genuinely did a double take on reading the word 'sister' because there is no sister mentioned in the OP, just a brother. Then the penny dropped. I feel as I do when I've seen trans right activists enthusiastically telling a parent to accept their son when the parent is in deep distress and struggling to know what to do about their teenage daughter who's always had all sorts of difficulties and is now convinced that identifying as a boy is the answer to everything. Denying reality is never going to end well.

Good luck, OP. You've had a lot of sensible advice on this thread.

I am estranged from a lot of my family because of one family member. I’ve chosen not to talk to them because they were feeding back to her. The only person I do speak with who has contact with them have agreed not to ever mention them. They don’t feed back.

He doesn’t sound like a nice person. I wouldn’t now get involved because your mum has because you’ll resent her eventually. Maintain the boundary as you have of not having him in your life. He sounds like added drama.

I'm sorry, that must have been really hard for you and your mum. My younger brother has shades of this, and its hard not to resent him for leaving everything to us other siblings and ignoring our surviving parent, who is in need of care to some degree.
I have tried to reach out a few times with no response and when we do see each other it is civil, i wouldn't describe it as warm, but it's not cold. I still have only love in my heart for him, and understand that his experience of childhood and young adulthood is his own and not mine.
You sound sensible to me. I think you are thinking things through carefully and working out your boundaries. This is also important when you have kids who have limited control over the situations they are placed in, and the dramas that unfold because of them.
I try to model what I want my kids to see in my situation. I talk to them in an age appropriate way about it. I answer their questions as well as I can.
I agree that you don't have to pretend to go along with the transition, and I think you'll find the best way to approach that. Your Mum must be struggling as well, and you are right to support her.
Good luck OP.

“My mother feels she has to accommodate his name/pronoun changes because she worries about his mental health and doesn’t want to be cut off, despite not buying in to the whole trans ideology.”

I appreciate your mum worries about him, & perhaps with reason, but it’s a basic premise of mental health support that you do NOT affirm a delusion.

That doesn’t mean challenging it at every step, but silent non-participation may be possible.

You don’t have to see him, of course, but there may be family occasions when you’ll all be there.

It’s probably a good idea, if you’re on good terms with your mum, to have a chat about what she can or cannot expect from you?

I think the phrase 'grey rock' might be useful for you, if you don't know it, OP.

Wise words.

Why so many deletions on this thread?