My son will take us all there and be our tour guide....
I sort of hate to wade into the weeds here but while I think that will be OK on Vatican property, the same may not be true elsewhere in Rome due to some licensing mandates. You don't say how many "all of us" is, or if your son will be acting as your guide elsewhere, such as at the Colosseum. A licensed guide overhearing your son impart historical/cultural information, especially if your group is of some number, at other sites may have issues with that and possibly confront the situation.
I'm not an expert on this topic but we have others on the forums who are, such as some posters on this 2014 thread, so I hope they'll weigh in.
https://community.ricksteves.com/travel-forum/italy/are-groups-required-to-hire-licensed-tour-guides
That said, if he'll only be your helper at the Vatican, it's probably moot point. There are some rules there regarding the need to use radio headsets for groups over of 11 participants, and he's not allowed to provide verbal instruction inside the Sistine Chapel but he likely knows that. :O)