They can, but this should be done very carefully. Many boats have bursted in the past while doing so.
Do the kayaks have to be serviced?
We don't have a regular service for them. In order to enjoy your boat for a long time, you should clean it now and then with fresh water and you should check the valves.
My husband weighs 260 lbs. (120 kg). Can he paddle the kayak?
There is no problem with regards to the buoyancy. The question is whether or not he fits in the boat. He would have to try one out for size.
What does self-bailing mean?
Self-bailing means that the boat has holes in the floor so any water which comes over the side flows out again due to the speed of the kayak. Only our white water kayak has this characteristic, though.