If I knew my family member or friend was vegan I'd automatically assume it would be a vegan menu, unless I knew their partner definitely wasn't vegan too. I know being vegan is often about more than just the food.
If they were both vegetarian I'd not be surprised by a vegetarian menu either.
If one of the couple ate meat and the other didn't I'd assume there'd be a meat and a veg option.
As a pescatarian since I was a young teen I'm used to going to places and not really having much to eat. I didn't eat meat in the 90s so quite accustomed to being given a meal just without the meat part, or to have the obligatory pub veggie options of the time. It's no wonder I hate nut roast as for a while it all there seemed to be! Even these days the options can be fairly limited, though there is usually something.
There are some vegan 'alternatives I really don't enjoy - much of the vegan cheese I haven't enjoyed, and I'm not a big fan of 'pretend meat.' But the rest I'd include in your average meals anyway.
As an aside if given a meat dish I would struggle. After not eating meat for so many years it's likely to make me feel quite poorly. I don't taste and texture of most meat - things like bacon and steak I've never been able to enjoy, even as a child, as they made my stomach hurt. However, if it was something that used meat stick instead of veggie I'd likely not know. As a pescatarian I do eat some animal products and I'm not overly watchful as for me it's a preference and not a lifestyle/ethical choice. But I hate being lied to over something having meat products in or not (just tell me and I will chose to eat it or not` and being told to eat meat would,likely lead me to be quite ill.
Both dh and dd love meat and eat it most days. But both would have a vegetarian or vegan meal if it was served. Whilst they enjoy meat they do also eat vegetables, etc. As well.
Serve what you want to.
People can decide whether the lack of meat upsets them enough not to come.
Tbh if they are the type to refuse over one meal you'd probably be better without them being there anyway.