It’s impossible to assume nothing.
Either they have done what you’ve asked, or they haven’t
Either they know about the issue already, or they don’t
Either they are lying to you, or someone else is
Either they are planning on coming, or they are planning on skipping it
Either they understand what you’re talking about our they don’t
The fact is, you have to operate with some assumptions when you plan, when you preach, when you talk to people, when you lead a project.
But it matters which assumptions you act on…
You can either think the worst of people. This is called “accusing” them. or you can think the best of them. This is called “trusting” them.
I reckon the best thing to do is tell them you’re trusting them, and ask them if your trust is well placed.