mine are unspayed, aged around 2yrs - I don't intend getting them spayed at the moment, but I may one day, although it would involve splitting up the group as I could only have 2 at a time in the house recovering - the rescue I adopted the group of girls from didn't believe in spaying, and although I was very pro-spay before I spoke to her, she made me think again.
Maa's had a couple of general anaesthetics already this year, so I don't want to put her through another just yet, and Tia is apparently very low risk for cancer, being a nethie. The risk is a lot more than toffeepudding said though - 80% risk by the age of 5yrs of showing some cancerous developments to the reproductive organs, some breeds being more prone than others, and mixed breeds being most prone to it.
However I'm not sure if spayed females live that much longer than 6 or 7yrs anyway, since rabbits are so fragile.
None of my girls have behavioural problems - they are all very sweet natured and Maa especially is like a little puppy, very affectionate!
If you can find a good vet, and be sure to ascertain that they know about rabbits (lots don't, believe it or not!) you are safe to go ahead and spay your girls - but getting a good vet is crucial. The only way it could kill them is if they had heart failure, which would really be a fluke of nature, and is rare, or if they got an infection, pull their stitches out persistently, get adhesions or stasis afterwards - so it's very important also to take a couple of days off work to nurse them and make sure they are recovering well. Also check your vet does internal, dissolveable stitches!