You absolutely should, morally and on principle, give equal shares to your dc.
That’s what every parent with a moral compass does anyway.
When it comes to wills, the money is much more than money. It represents love.
And you wouldn’t be so upset by the estrangement if you had no love for this adult child.
Also, if you give unequal amounts, you die leaving your siblings set up for a life time of antipathy between them. If you give them equal, they st least have a fair crack of carrying on their relationship on an equal footing.
I have seen so many rifts between families over wills. A recent example was where a parent left more money to her adult children who were struggling financially, then to their adult child who wasn’t rich but had a good professional job. Little did this parent know, that the child who had been doing better, had been paying consistent substantial sums of money to help pay off his siblings mortgages. And then he got rewarded with a token amount by his parent, did the siblings pay him back for his kindness? Like hell they did!
Lastly, your estranged child is still your child op. Relationships may change but that will always stay the same. They emerged from your womb. And as such have an equal moral right to your legacy. In many countries, unlike in UK, this imperative is enshrined in to law.
Be the parent and the bigger person op!
Take the higher path!
Estrangement for no reason is a painful kick in the guts but leaving them equal amounts will prove more than ever just how misguided they were!
Good luck with your decision. 💐