You don't say how much tandem experience you have, but I can think of two things you might want to consider:
1) A sore butt is more likely on a tandem than on your single until you learn to stand about as much as you do on your single. It will affect both of you.
2) In general, when compared to cycling alone, riding a tandem is more difficult for the stronger rider and easier for his or her teammate. The effect seems to be especially true for new teams and diminishes with experience. Although you are confident in your ability to ride 150 miles on your single, riding 100 on a tandem may be harder than you imagine.

Yes, practice on the tandem quite a bit. As you gain experience together you can decide together whether a ride to see your family is a good idea... or not.