Thanks for all the responses. I’ve checked that it is fine to fly over the US with less than 6 months on passport and Mexico it would of be fine too if flying over too and then it suddenly dawned on me whether Princess would let as board. Finally manage to get hold of Princess and they have confirmed that passport needs 6months after the end of travel.
Booked in for passport renewal this coming Monday so hopefully still plenty of time to get ESTA.