Giving Money for Deposit on Home to Children

Could you present it as an interest-free loan, rather than a gift, with a provision in your will that after your deaths, any outstanding amount of the loan should go to your DD first and then the estate divided?
As others have said, you don't know if any or all of your wealth will be needed for care fees in the future, but it might be more acceptable to your DD that way and prevent hurt feelings.

Could he purchase a small place somewhere in outer London, and commute. I must confess I wouldn't be entirely sympathetic with anyone wishing to purchase in inner London. They would have to work their way up the property ladder for that.

Then help your son and tell DD that you will make sure that things are evened up in your will.

There is a similar situation with my family, but the one who is well off always refuses a handout when another sibling has need and is on the receiving end of a gift.

It is difficult isn't it - we love them all and only want to do the right thing.

My SiL might but my DD is quite a jealous person. She used to keep bringing up the fact that we paid school fees for our DS throughout his schooling & hers through secondary ( we couldn't afford to pay hers at primary level). However, as we point out, she has been more academically successful.

If she found out we were considering giving him a big chunk for his deposit, it could estrange her. Not pleasant, but a fact.

I would help son now, whatever is left can be divided equally if you wish

I am wiling to bet that if you asked DD and her lovely caring husband their opinion, they would tell you to go ahead and help your son, and they wouldn't mind at all if you never evened it up.

You can help him now. Perhaps at some time in the future, DD and SiL will need your help too. Cross that bridge when you come to it, and do what you can for DS while it makes a difference to his life.

Help them out, where you can, as and when need arises. Don't go too heavily into what's fair. Who knows what the future holds for the other one? And who knows how much will be left for them when our care costs are taken care of? Don't overthink it.