Rabbits are most active at sunrise and sunset (and the hours surrounding these events). They generally sleep during the day, and they nap intermittently overnight. So, if you’re letting the rabbits out during the middle of the day, that might explain their laid-back behaviour. It’s true that, at 6 years old, these rabbits aren’t teenagers anymore (young rabbits can really be crazy-energy), but that shouldn’t make them total lazabouts… My rabbit is somewhere between 9 and 12 and he definitely has his moments of energy-burst. But really, all rabbits are individuals – maybe you just have a pair of couch potatoes, like you said.
A few words:
Fabric, if ingested, is indeed very dangerous – deadly, even. But you have to treat your rabbits as individuals. If your rabbits weren’t eating the t-shirt, you don’t have anything to worry about. My rabbit would be devastated if I took away all his fabric. We give him hand towels: they’re not only comfy beds for him, but one of his favourite toys (he bunches them, scratches at them, smooths them out, etc.). A 100% safe, sterile habitat isn’t possible: every day or so you have to check their belongings to make sure they aren’t mistreating them and potentially endangering themselves. Fabric is no exception.
Don’t be afraid of greens. Pellets – even quality pellets – are pretty junky and should be restricted. Rabbits need fresh greens to get a balanced diet. Serve them dripping wet and they’ll also be drinking water. (Of course, grass hay should make up the most of their diet.) Lettuce is a little iffy because so many lettuces are white/light. These kinds of “greens” definitely will lead to diarrhoea. Look for dark leafy greens instead. Romaine is a very healthy green to serve, for example.
Bring your rabbit to the vet regularly, like once annually or even twice annually. A rabbit-savvy vet is necessary because so many vets have never studied rabbits yet they are significantly different from cats/dogs, and lots of errors resulting in death have been made. An annual check-up should include a physical exam, a dental exam with a scope, a feces sample test, a blood test, and a urine sample test. You can perform physical exams yourself at home every few months.
I’ve compiled a list of great online rabbit resources on this website: http://torontorabbits.wordpress.com. Just look in the sidebar under “Rabbit Info.”