I wouldn't let them near the baby either, and if it were me I would have the hard conversation and tell your boyfriend why. They chose not to vaccinate and it is your right to keep their kids away from this little baby.

It isn't just measles to be worried about, think about all the other diseases they are not vaccinated from. I know someone whose baby contracted meningitis just before their scheduled vaccination and the baby became partially blind and has a disability now.