I second that. Girls that just broke up will only use you as a rebound, no matter how honest they might look.
The one that doesn't seem to suit you, she probably doesn't. Try to hang out more with her to see how she is, and if it doesn't look like you two fit then just keep her as a friend. Either way, it shouldn't be very hard to keep her as a friend if she's not so interesting.
Be there for your friend, the one that broke up with her boyfriend. Give her some time to recover, then you can start dumping hints that you like her.
It's quite easy, compliment her on simple things you like about her, stay honest the whole time. Don't over do it because it will look fishy.
Since you've been friends for quite a while, it's true it might not work out between both of you.
Besides, telling someone that you love her WON'T break a friendship.
Oh and Cyber, if you don't try you'll never know. Waiting for someone to make a move when you have a crush on them is just painful, and if everyone was waiting nothing would ever happen.