Manipulative Older Half-sister May Sue For Inheritance — Recourse To Get Ahead Of This?

So, in a slightly large nutshell:

I am 34, my half-sister is 54, and my half-brother is 56.

Our father (85) and my mother, no blood relation to half-siblings (67) have discussed my inheritance with me in recent months. They’ve told me flat out that I’ll be the sole beneficiary of my mothers life insurance policy (very sizable), that I will get 50% of whatever their paid-off house sells for, and 75% of an inherited Roth IRA (also sizable). I also live in a property with my partner which we pay the mortgage/taxes/utilities on but which is in my mothers name (she helped with the down payment), and that will also be transferred to me in the trust via the deed. A revocable living trust is what they told me they have, with the executor of the trust being my cousin, who used to be an attorney and is now an investment advisor. And if he can no longer act as executor, they have an attorney/family friend who will be.

Their reasoning for my getting the “lion’s share” is the following: I’m the youngest sibling by 20 years, having faced mental/physical hardships that hampered educational goals/delayed career progress for quite some time, and my half-siblings are both married, have grown children, and are living with middle to upper-middle class incomes. Also, my mother believes (and my father agrees) that she contributed significantly to their investment portfolio and being my birth mother, she has ample say in who gets what. Not to mention that even while I was growing up with seriously older siblings, both of my parents were very generous with helping them financially and in other ways.

This past summer, out of jealousy, my sister (who I have not spoken to in 9 years) sent me numerous text messages from her husband’s phone telling me how my parents are in “cognitive decline” and that she and I should really should establish a relationship again, yada yada. Coincidentally these text messages came after she found out via looking on my Instagram (which is now private) that my partner and I moved into a house, and she put two-and-two together that my parents helped us with the down payment. Her reaching out was seen by my parents (who are both still working and have vibrant social lives and are not at all mentally incapacitated) and myself/my partner as a blatant attempt to construct some sort of narrative to use to her advantage someday. We’re all thinking that when the time comes she may try to pull something—say that I had “undue influence” over them as I live only a few miles away and lived at home the longest and she only sees my parents a handful of times per year.

I don’t foresee my half-brother starting any sort of drama (he’s estranged from the sister as well and mostly keeps to himself). But my sister has a history of manipulative behavior—in her previous marriages she was in and out of court more times than I can recall. Needless to say, I don’t want any drama with her. My parents however are refusing to disclose her share of the inheritance preemptively because frankly they’re tired of her behavior. My dad has told me there’s a no contest clause in the trust, but I know you can essentially sue someone for anything.

I just don’t know if A) any attorney would even take her case without substantial evidence (I’m not sure how manipulative and conniving in this aspect she could be), and B) how long she could potentially tie-up the dissemination of funds from the trust by claiming some horseshit.

I also don’t know if it would benefit me to speak to an attorney while my parents are still living in order to explain the situation / hypotheticals and why I’ve chosen not to speak to her (including the fact that she’s made homophobic comments in the distant past).

Does anyone have any advice on how to approach this? Thank you so much, sincerely.