"AIBU to remain no contact until she is willing to come to me and discuss this?"
Yes, that would be unreasonable. You would NBU to go no contact, if you chose. You would NBU to see her if you chose. You would NBU to raise your own discussion with her or anyone else. You WBVU to try to manipulate the situation , so that she must come to you to raise a discussion of your choice.
"The problem is I’ve got a feeling I’ll be waiting a while."
Yes, I do too. Which is fair enough, given the unreasonability of manipulation. 
"How would you proceed in this situation?"
First of all decide if you wish to go no contact, or not.
Whichever you decide, then tell your parents (in person, by email, by letter, however you are comfortable doing)
- That you really, really don't mind how they distribute their estate - be it that they spend it; leave it to your sister & your children; leave it to your sister entirely; or even leave it to the local cat rescue - you really don't mind!
- What you do mind is hurtful jokes that seem to be emphasising how far down the 'love' pecking order you are! While it's fair that they should have their own preferences, it is not fair that you should be made to hear those preferences.
Either 3 (if you want to go NC). That you have therefore decided you'd rather not see them, but you wish them well.
Or 4 (if you don't want to go NC). That you would therefore like to ask them not to mention their estate to you again, to accept that you are a 100% happy for them to do with it what they wish, and are 100% happy for them to make all their future financial and care plans with your sister.
That's how I think you should proceed.