We just went through this about a year ago when my daughter got married. The invitation will say ‘X and guest’ if they are allowed to bring a date. This is used only for not married people. If the person invited is not allowed to bring a date then the ‘and guest’ is not on there and you assume you can’t bring a date. However, I’ve not really experienced that although the instructions for it were in the wedding books. I wouldn’t ever do that, personally. I do realize that it can cost a fortune for a wedding so every person adds up but to me I’d probably cut the person from the guest list rather than tell them they can come without a guest. Of course you might know someone well enough to know they don’t have a plus one and don’t plan on getting one just for a wedding so you would leave the ‘and guest’ off in that case and it wouldn’t be rude or tacky. If you are inviting someone who is married it’s ‘Mr. and Mrs.’ or whatever is appropriate for the couple. If you want that couple and the kids you add ‘and family’. I’ve never heard of a situation where you invite a married person but not their spouse. Not sure the etiquette for that since it seems seriously wrong.