To me, the important thing about the will is the way it propels the story. It provides opportunities and challenges for the MC (and some of the other characters) which can advance the story. It's important enough to be a priority, but not so important that it automatically drowns out any other priorities. That's a very useful tool, as long as the audience buys in.
I agree that the audience probably won't hold the will to an exacting legal standard. Most of us aren't lawyers after all. What matters is that the will is presented consistently. In the end, the will provides rules that will guide the choices available to us. As long as the MC asks the obvious questions and gets understandable, consistent answers, we'll have what we need.
I do think it helps to keep up a token level or realism; it would be distracting if the will conditions required the MC to commit a felony, for example. But as long as the conditions don't venture too far into the weeds, I think we'll be buy the will as presented. It's then a question of exploring any potential loopholes, making our choice, and seeing what happens (possibly with a couple iterations if we get more information before having to make a final choice).
Basically, as long as the will is a means to highlight the MC's cleverness or define his priorities, I think you'll be on solid ground. If becomes a means to throw an unexpected monkey wrench into the works (especially at the last second), that's when people will suddenly start burnishing their internet lawyer credentials.
Come to think of it, it's a bit like Sanderson's Laws of Magic - just for an
extremely mundane type of magic.