Major writing issue - need help

I'm starting to plot out the sequel to Unreachable and I've come up with a major snag and I haven't even written word one yet. See, Unreachable and the Christmas story are both written in the first person. Now I have this sequel, which is going to be even more complex, and am wondering if I "HAVE TO" stay with first person because it fits the series. Should I swap to third because it would help tell a more complete story. Can I swap back and forth between chapters when I need to show action outside of Ms. Rosenthal? Thanks for the help.