Our will/s cover what would happen if one of us dies (everything goes to the other), both of us die (everything goes into trust for the kids, with 2 trustees) and if all of us die - in this case, the estate gets split 50:50 and we have each appointed who we would like to give the money to and what proportion to each (parents, siblings etc). You could consider doing something like this. I don't think most people, unless they were very wealthy, would be looking to give away part of their children's inheritance to financially independent adults. That seems a bit crazy while the children are still young and dependant, perhaps things might change once they are adults and set up properly.
ETA: is there any non-cash item that your DH could will to his mum and/or sister you make him feel like he is looking after them. E.g. a car or caravan or collection of some sort? These items can be a hassle for your executor to have to sell, but do have value. Might make your DH feel better to be giving them something 'worth $10k' (just for example) but that won't feel like as much as $10k cash to you.
Edited by Jersey Caramel, 15 May 2019 - 04:32 PM.