Besides the security line, do we need to wait in any lines to get into basilica? If we have tickets into the museum, will that get us into the basilica any easier?
“Museum,” as in the Vatican Museums, which include the Sistine Chapel? If you have a guide, when you’re done with seeing the series of museums, finishing with the Sistine Chapel, your guide can escort you through a door that only guided visitors are permitted to use, then down a long, ornate hallway that leads to the basilica, bypassing the long security line for it.
You’ll have gone thru a security screening as you enter the Vatican Museums, but that should be a relatively fast process. So if you’re visiting the museums and basilica on the same day, it’s easier and overall quicker to start with the Museums and finish with St. Peter’s, as long as you’re doing it guided.
Unguided, you can get into the basilica as soon as you’re through its security line, but you’ll have two security lines - one for the the basilica and another for the Museums. And without the “shortcut” exit door at the back of the Sistine Chapel that only guided visitors are permitted to use, you’ll have to retrace thru the Museums back to the entrance, so it’s more time and more walking … not easier.