is it possible to use two RoomBoards, with SHT-1x only on a single JeeNode? I am only interested in temperature and humidity (no PIR or LDR).
An would it be possible to connect them by 2-5m shielded cable?
Yes, that should be feasible. You need to add a 0.1 µF cap between VCC and GND. I once saw an example where someone connected the SHT11 via a 10 m cable that way.