I am trying to advise relatives who will arrive from Iceland at LHR terminal 2 at 11:30, would like to use the AA lounge in terminal 3 (since they have day passes), then will leave on a flight from terminal 5 at 15:30. Have never been to these terminals, so am wondering if it is easy enough to get from T2, to T3, then T5.

Upon arrival I assume there will be a required immigration checkpoint; will it be necessary to first go through immigration...or can it be bypassed since they will not be leaving the airport?

Any advice you can provide about how easy or difficult (going from T2, to T3, to T5) this will be - and how much time will be needed, would be appreciated.