Honestly I have never seen dancers being bothered by non-dancers (unless they invade the dancing area). There are pros that take up seating space and may end up dancing one or two at tandas at bestThanks everyone, sounds to me like it's probably fine for them to come if they want to - I am not pushing for it but even though it's their idea I think they will get bored after a while so I'll make sure there is an exit strategy.
I'll look into classes and offer to go to those with them, even though I doubt they will take me up on that.
The main reason I asked is because this will not be one of my local milongas, I am the one visiting their city, so I don't know what the milonga will be like in terms of atmosphere/friendliness; and likewise, I won't be able to introduce them to any of my friends because I won't know anyone else there either.
This is the kind of thing I wanted to keep in mind, how to bring non-dancers along in a way that doesn't bother other dancers, and that's what's tricky to figure out when it's a milonga you've never attended before. I will probably end up asking the organisers for advice on where to sit.
When I have taken non-dancing friends, I never tried to get them to take a class or teach few steps. Neither was I interested nor them. If they like what they see, you can hook them with the host, who is likely an instructor or knows right direction to point them to.
I will not overthink this. If they want to tag along, I see no issues.