Our daughters are traveling to Paris, one under 18. We are considering buying the museum pass, but the minor is free to most places. If we just buy one pass, will they be able to enter together, or should we buy a pass for both?
They will not need two passes. Depending on how old the under 18 one looks, they may not even ask her to prove her age but if she has a license or other ID that shows her age, she will be fine.
If your daughter is an older teen be sure she has ID; we carry a copy of the Passport. Kids just walk in with parents everywhere except Invalides and the Arc du Triomphe which usually don't have huge lines. Kids pick up a free ticket there.