My late wife was a wills and trusts attorney. You need to talk to one of those about a “special needs trust”. At least that’s the US terminology.
It sounds like your goal isn’t really to (partially) fund your daughter’s life. But rather to (partially) fund the care of the daughter’s disabled brother in law and crazy sister-in-law. A trust can arrange for that to be the purpose, your daughter to manage it, and include contingencies for things like your daughter and her husband gets divorced or he dies early or …
A thought to consider is to simply fund the trust with your entire assets when the second of you and your wife die. Zero to the two well off brothers, zero directly to the daughter, all to the trust for the unfortunates needing care. That totally solves the “treat your kids differently” problem. The trust can also specify what to do with the trust assets when first 1, and then both invalids have died.
Simply willing money to the daughter leaves way too much to chance. And can subject her to inappropriate pressure from her in-laws.
The truth is your estate of CAD1,5M ~= USD1.1M is large enough that folks used to not much wealth will be sorely tempted to spend from it as if it was infinite, replaceable, or self-refilling. Which it is not. Which spending would rapidly turn your very kind actions into precious water poured onto desert sand. Even if spent solely with the intent of benefiting the invalids, e.g. a paid-for house for them to live in, etc.
At the same time, it’s not very large as endowments for life care go. Especially not split between two invalids. Invested appropriately, it can provide a USD50K-80K total stipend (so USD25K-40K per person) year in and year out to partially fund the lives of the invalids. So your goal is (or at least I advise that it ought to be) to have the income / growth of your principal care for them to the extent it can, but be very circumspect about letting the trustee spend down principal until very late in the invalids’ lives, if at all. It would be easy to shrink the principal through well-meaning spending to the point that the income becomes derisory compared to the cost of care of the beneficiaries. That is a very common, and very bad, outcome. The money runs out just as everyone involved is getting old.
And yes, whatever you do, you need to have some heart-to-heart discussions with each kid separately and all together to come to a plan that works for you without triggering hate from them. I bet you’ll find the better-off ones aren’t too worked up about it. The largest share either brother could expect is 1/3rd which is ~USD350K. That’s a darn nice gift, but it’s not going to move either of their financial needles appreciably.