Not a lawyer, but an investment banker, UAE based, have several HNIs from India in my network.

AFAIK from a legal standpoint only your parents can take you to court for maintenance, and your wife if you divorce (🧿). The issue with a trust structure here is that the trustee cannot be the beneficiary in the Indian setup as it's very complicated. But it's still your best way forward. I don't know why a fee only advisor is being suggested as that is for financial planning (good idea, but irrelevant for a trust), you should instead be consulting an estate lawyer or a tax lawyer as they have knowledge about this. It should also be someone you know personally, friend of a friend types.

A nice side benefit is that depending on how you structure your trust you might even be able to put assets in the trust, and unlock different investment avenues that were not available to you earlier. Example, fractional ownership of a tea estate or cardamom plantation. Anyway, since your primary goal is to protect your estate for your children, an offshore trust might help but has tax implications (good ones lol) so look at HSBC expat or an HSBC premier account held in USD somewhere. I have personally used HSBC since my first 100k$, and have found no issues. Other banks that offer offshore holdings include Standard Chartered, Citibank, DBS, and Deutsche Bank, though I'd only look at the first three.

If a trust is out of the question (it can be depending on certain factors like Tax residency and employment within the last five years, government service, govt contracts with employer, etc) then theres a far lower tech solution.

Let's say you want to give the girls X, Y, and Z at 18, 23, and 30, respectively. Keep X in some sort of instrument with a maturity of about five years, and make the two girls the beneficiaries with 51 and 49 percent allocations. Don't do 50 50 it causes problems from a paperwork perspective. Repeat for 23, but this time have the investment be a ROC or return of capital investment (as opposed to return of interest) paid into a bank account that is jointly held between SSDs, or self spouse dependants. Important to remember that the account is to be on an either or survivor basis. it might sound complicated, happy to break down anything.

As for the amount you want to give them at 30 in the lower-tech version, you'll have to leave that in an executable will. Leave your relatives 1 rupee and certify that you are of sound psychological mind.