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

In other words it's the same person, just with a bit of lippy on.

Support needs to go both ways, and backing your mother into a corner buy putting pressure on her and requiring her to accept and validate that her son (says he) is now her daughter is not what I would call particularly supportive of her, is it. How long ago did her husband die? Is she vulnerable at present, and might that be a reason suddenly to decide to coerce her back into his life?

@Rimding

Sorry if i missed it but I don't get it.

You are NC.
Presumably neither of you wanted a relationship for whatever reason.
That status quo was maintained for a long time.

Just because your brother suddenly wants contact now doesnt mean you have to agree to it.

He couldnt be bothered to get in touch when your father died....why now?

Personally I'd stay NC let your mum crack on if thats what she wants

Surely you quite simply say you stopped contact for xyz reasons/ behaviours. That hasnt changed, they still did those things. You do not want to reinstate contact. What your mum does is up to her. Transitioning or not makes zero difference.

Of course, women should only be seen and not heard.

In supporting your mum, I would think also about what support you are willing to offer outside of what your relationship with your brother looks like.

For example, if every time you meet up with her she is telling you all about what he is doing, or offloading about unreasonable stuff that he is doing/saying what do you want to do?

I personally have a very low limit on hearing about the latest drama in my step-brother's life and keep any chat about him and my step-dad very superficial. Not my circus, not my monkeys.

I deal with this by adopting a persona. I don't say anything that will trigger them, I don't engage or get pulled in, and I keep my thoughts to myself unless they are going to be helpful and well received. I basically keep the peace, regardless of what I think privately. So there's distance there but I don't think they notice it, though I expect others do who know me well as they can see I'm far more reserved when they are around. I lie by omission and I'm ok with that.
I see absolutely no point in engaging in opinions as we're pretty much at opposite ends regarding transitioning and we'd never agree, I do firmly believe that people can dress and present however they want and I will call a person by their chosen name. I avoid pronouns like the plague. I've no interest in drama, and I know my relative loves drama and actively looks for opportunities to create.
I've been supporting my elderly parents because they went into this with open hearts and arms but without planning for how this could go, given that they know this person of old and this leopard has only changed his dress, not his spots. They get very upset if they think, or are told, that they've said or done the wrong thing. It's really hard, I hate seeing them agonising over what they could do differently when there's nothing, simply because the person is looking for issues and will make an issue even if nothing actually crops up.
I wish I'd had more of a frank discussion early on about how they could deal with this and that they have some choices, and to hold in their minds how they dealt with this person previously. They are wrong footed and upset after every interaction, but this is because my relative is quite combative and is actively looking for offense or 'wrong words', iyswim. So my role is basically to calm them down and put some perspective in and comfort really. I think this will eventually settle down, I hope so anyway.
I definitely would not allow access to the kids, but equally I wouldn't miss out on family occasions to prevent it. My nieces are told that our relative just likes wearing what he wears and that's fine, and we use only his chosen name, never pronouns, and he's not given a title either (it would be uncle, he'd prefer aunt), name only. And their parents just limit any direct contact when the family is together, opposite sides of the room, only a few mins chat etc. They've not announced anything to the rest of the family, but it's pretty apparent what they are doing and I think they've had a quiet word with a few of the wider family who might otherwise have gone big on the 'oo here's your aunty' type of chat with the kids. The kids are too young for a frank discussion of the ins and outs of trans people.

He'll still be a horrible person as a transvestite.
I'd keep well away from him.

well I have been told by the Op that I’m absolutely wrong!!

Hi OP
it may have been mentioned elsewhere but I’m worried your brother may wish for involvement with your children in an ‘aunty’ role. I have not experienced a transitioning brother but I’ve certainly experienced a callous one. To have any contact with them- eg at my mum’s, Christmas etc- I had rehearsed exit lines, plans with my DH and boundaries I would not allow to be crossed. And I would always have an exit strategy.

But before any of that I had to decide whether I wanted contact. In my case, I did.

In your case - well it’s all on his terms isn’t it? You haven’t decided you want to see him again… he has. And why? To apologise for his previous behaviour? To make amends and heal relationships? No. Its to show off his shiny new identity and watch you all squirm as he rubs it in your face and your children’s faces.
His gender may have changed but his character hasn’t. Stay well away.

I have to agree. I find it hard to imagine a mother so uncaring towards their child that they would only be nice and welcome a relationship with them due to societal pressure rather than parental instinct.

That's very telling isn't it? There's lots of good advice on here - one thing I'd add is that if he's already spoken to other extended family ,members but not you, he may be setting you up to be the baddie? Which is another reason to grey rock him. I think someone suggested "polite indifference" .

You can be polite, say nothing that would allow him to weaponise and focus on you and your family. If further down the line it becomes apparent that he's genuinely remorseful for his previous callous behaviour and isn't spending time policing people's pronouns etc, you can always change your approach.

But you were estranged for a good reason.

Do you think he might ask her for money? I am glad you’re there to support your dear mum. Just be cheerful and supportive and let her talk about what he’s like etc when she does see him. Play the long game x

So she’s being nice and accepting to him because of society pressure rather than a mother simply over the moon her son is back in her life?

Ok 🤷‍♀️

He could be wanting a relationship now as he felt unable to when your dad was alive. He may of felt your dad wouldn’t of accepted him and now he is gone he feels he can be himself with you all.

If your dad’s death is recent I think it’s reasonable for your mum to say she is not in the headspace to meet up yet.
There is no rush and a way to support her is to ask family to allow her time.
I would suggest when they do meet it would be outside the house until you’re sure it’s a good relationship for your mom.

To be fair, the way the Op said brother went round and secretly canvassed all the extended family coming out to them first and telling my mother last. certainly indicates that she also thinks there was an ulterior motive

People can want whatever they want. Other people are not obliged to give it to them.

This is nonsense, sorry. If someone 'coming out' on their own terms makes them a shit, then good lord the bar is low. My brother came out to our aunts first, then friends, then me, then our sister, then mother, then dad and then grandparents and wider family - thought there are still some he's never bothered telling because they're homophobic scumbags. Doesn't mean he was building a 'compliant army' for crying out loud - just being sensible and safe with who he told he was gay. Coming out as trans is not different from that perspective.

i have a brother I haven’t spoken to or seen in 10 years. My mother still sees him on the regular. Initially she went on and on about how I was making things difficult for her but I just held my ground and said I wasn’t stopping her seeing him but she had to respect my decision to no longer engage with him. My brothers’ not trans but the same approach applies. You can support your mum but that doesn’t mean you have to have anything to do with him. If you were estranged before I’m sure him popping a frock on hasn’t erased the issues that caused the estrangement.

It’s sad she is definitely feeling the social pressure to make nice and be tolerant.

It will be because she is a mother and so relieved they’re not estranged anymore, not societal pressure.

Oh right - then in that case I wouldn’t give this any more thought.

Just reiterate to your mum that you are there for her and her alone.

And don’t ever be tempted to have any kind of showdown with someone like this.

oh and keep your kids away needless to say