DH always discussed our financial affairs with DD as we can trust her she's been to university and is very clever, she always knows what's best to do and DH always said she had a better grasp of these matters than I do as things were different when we were younger.
You have me completely lost here. What has having a degree and being clever got to do with trust or knowing the best thing to do? Our prisons house many people with a whole raft of degrees who are as devious and untrustworthy as they come and have devised and run the cleverest of scams.
What I read from all this is that your DD was Daddy's little girl, his favourite and, yes, she is clever, she knew exactly how to wind him round her little finger and how to extract money from him whenever she wanted it..
It seems to me your DH wanted to dominate the life of his son the way he thought he had his daughter at his beck and call, but your DS was man enough to decide to make his own life, to marry someone whom he loves and your DH saw your DiL as an implacable enemy from then on.
You say that your DS and DiL have been married for 20 years. Yet you still say I don't want to go against my dh wishes and have outsiders taking our money and leaving our family high and dry Where is the evidence that after 20 years of marriage, the moment you die and your son gets some money his wife is going to upsticks and leave him, tucking your DH's money in her back pocket as she goes? The whole idea is totally absurd.
Your DH and DD have successfully brain washed you over the years to believe without any evidence that your DiL wants her FiL's money and your DD has encouraged that idea while raking in as much of her father's money into her own pocket as she can. If you left everything to her, her brother has as much chance of seeing any of that money as finding the pot of gold at the end of the rainbow.
The good news is that now, you have, sadly, lost your DH, you are beginning to see the lack of logic in both his and your DD's arguments. Making a will is a personal and private issue and none of your DD's business. Leave your money as you think fit. This obsession with your DiL running off with it, as just that an obsession and, like most obsessions, has no basis in reality.