HM I don't know anythig about adoption other than the fact my niece and nephew in law are going through the process at the moment and it takes ages. They have to be vetted from every angle and undergo a lot of training - and this is even though they have 3 children of their own already!
I'm only saying this because I would imagine that any evidence you can provide as to their character would form just a small part of the case for or against their approval or otherwise. And I really can't imagine that the adoption people would ask whether you think they would be good parents - that's incredibly subjective (as anyone who spends any time at all on Mumsnet will have noticed!) I would expect that you would provide, as the descrption states, evidence of their character, not your opinion of how they perhaps might tackle one of the most life-changing of all experiences. So, "how do they cope with pressure", "Do they have a strong relationship" may be more like it, rather than "Would she still live away from home 3 days a week if she had a child to look after" - how the hell would you be able to know that?
Questions like that, if you are a friend, should be simple enough to answer honestly, even if the answer was "I don't know". It may be an idea, if you're worried about it, to see if you can find out the sort of questions you may be asked before you decide whether to proceed.
I'm sure you don't want to prejudice the case against your friends but, like many posters have said, I couldn't imagine life with kids before I had them. My life has changed 100% and my priorities have changed accordingly. Everyone's do. Even your friends'.