I did that the other day, well got DF to do it cos he is a bit blunter with getting times, dates, confirmation. But we got a "We will see" from one which we will have to follow up again. The other set is coming to visit, as they already had that holiday planned before we moved here. As for the next visit, that will take more invitations.
What has made me question what others do is that both my parents families are drop in for a cuppa people and the phone is there to keep in touch, regularly. So when my family rings they always ask if DF's parents are coming for a visit, have you heard from them, etc. because my family see them as a part of my life so are being polite and taking an interest. Then I always get a "Oh" response when I say we havn't seen or heard from them.
My family are drop in people even if you are just passing through town on your way somewhere else, you stop in, so I am trying to get used to this different way but not realy understanding it.
Hope that made sense.