I think post explains why I think the split should be equal as well as one of your posts further down.
Your son and his partner have chosen careers that dont pay well.
It is their own choice. But it is your daughter who will pay for that choice.
And your mum will be funding that choice.
I was also given less by my parents as " I didn't need it" cos I had " a better job". And my siblings need more help.
What I do have is a job I hate that I wish I could quit and leave but have no choice but to keep working for now. I don't have a choice because no one is funding my choices or my ability to make a " bad choice".
Same with your brother further down. You say your mum and you keep giving him money- that's partly why he needs so much cash from you. No matter how much you give him he will always need more. Same with your son- he has made the choice tp have that career and same with his partner- it is their choice.
And by funding that choice you are likely putting them on the path to rely on more funding for their " bad choices"
My.mum helped my younger brother with his mortgage. Helped with deposit. And then helped him pat it off years early. He goes on regular holidays abroad etc which is fine. His mortgage has been paid off for nearly 10 years.
All the time I've been paying off a huge mortgage and moved house about 4 years ago into a suitable house for the family. Still paying off the mortgage got 20 years on it.
But my brother complains how he can't afford to move house into a house with a drive and back garden- he's currently in a huge 4 bed terrace. Small back yard. And complains how mum pushed him I to buying the wrong house and now no one will help him buy the next house. ( After enough bad decisions mum finally decided to stop funding his crap decisions. He actuallybought a holidayhouse abroad.)
He never had to struggle to buy his first house and doesn't have the ability to save and work to move up the housing ladder off his own back.
Think you can tell this is a sore subject for me.
Your daughter will probably resent you. And you don't know what can happen in the future. I could fall sick tomorrow and my family would have to sell the house and our lifestyle would change. ( I've got insurance so the house will be paid off). But my parents weren't to know any of this when I was at University.