It's so kind and hospitable of you to want to invite new neighbors to dinner. Such a rare treat in this day and age to be asked to someone's home for a meal. My dad and sister are vegetarian, but there are things that agree with him that don't with her, so my advice to is to ask. They may or may not do certain foods because they simply don't take care for them, but they probably would hesitate to be picky if invited.
Mexican food is easy to fix and please everyone--you can keep the meat separate from the bean paste and everyone still gets a protein. All the other condiments can be built into tacos or nacho salad. But do ask--some people like salsa, if it's not too spicy. I'd suggest a fruit salad or a bowl of berries as a side dish.