I’m sure someone has already said this, but the easiest thing would be to split equally between your 3 children and the 2 that are married/have kids can then decide to give your GC something.
Option 2 is to split equally between all of them, so each ‘family’ gets roughly the same amount of money. IE.
Split your estate between 17 people
DD 1 with 4 children = 5 people
DD 2 with 3 children = 4 people
DD 3 with no children = has no kids but would get 4 peoples share.
So say if your estate was worth £17,000
Each ‘family’ would get £4000, with an extra £1000 for the 4th child of DD1 - I’m sure there would be no arguments over all the grandchildren getting the same amount from DD3.
Option 3 is to leave a set amount to each GC - say £20,000 and the remaining is split between your 3 daughters.
Either way I wouldn’t leave any of your children out of the Will. I used to work for a bank and it can get very nasty. Even if you think they don’t need the money - they may not need it to pay bills but they can have a bloody good holiday on your behalf or maybe buy a beach hut or something to benefit them in other ways. Ultimately you had 3 children that you aren’t estranged from, they should all be treated fairly and not forgotten.