Skysue; if you are uncomfortable, don't do it. Sounds simple, but it's the truth. Either tell dad straight up or just be "busy" everytime the invite comes up.
As for my clientele, I would say that I am friendly with them, but not friends. I have a few of them on FB, but don't socialize outside of that. That being said, I can see becoming more than acquaintances with one family. We have been invited to their daughter's baptism next month. Not sure if we will attend or not.