Let's not keep making the mistake of assuming Trump's tweets have force of law. He's just talking out of his ass again, just like he's not actually invading greenland and canada. Notice how he's talking about at least 4 different actions here, I'm pretty sure none of which he can actually do. 5 if you count thanking us for our attention to this matter (?). If Trump tries to do anything in this regard no judge* will uphold it.
Let's not keep making the mistake of assuming the rule of law matters at this point. If he does something and nobody stops it, its legality or lack there of is moot. If he says to do something and people do it and nobody stops him (or judge's rulings about it are ignored), then it doesn't matter that it was illegal.
I know you're just trying to get people to calm down, but at this point, people are right to be scared and right to think these things could actually come to pass considering it has happened before. Maybe it won't get that far... But plenty has already happened that should never have happened, and the US currently has a president who is illegally, specifically unconstitutionally, holding office and was allowed to be sworn in anyway, so it's probably not a good idea to assume this won't happen just because it's also unconstitutional.
People in power do what he says. His word is de facto law, even if it’s illegal. It literally does not matter. You are in denial if you think he’s not going to get away with this.