No I doubt there is a really good way of eliminating odor. In fact I do both of what you said not to mention - that is feed in a seperate tank (I have one nicely positioned next to it that is currently empty) and I change the water once a week or if I'm lazy I'll do it once in 2 weeks. There is pretty much no odor and if I wanted to drink a nice salmonella odor-free drink I could dip my head in it 
As for your 2 females trying to mate.. not sure what to think because my 2 males also mess around like that too. It's annoying wouldn't you say?
Both males I got about the same time.. the males I have, have very long nails so know their males. One has grown bigger then the other and that one is more laid back and relaxed. The smaller RES (about 6-7 years) is always mean to the bigger one! Sometimes he messes around like tries to mount the larger one (who isn't that much bigger, and is male) or does the flutter paw thing...
What I hate is when the smaller one bites the bigger one. It seems to be frustrated or something. Right now I seperated them and kept the smaller male in the smaller tank I feed them in (which has a filter and heater). I don't know what to do.. if I put the small one back in, he starts biting the larger RES when I'm not looking usually at the evening time.
And this only seems to be happening now that it's getting near winter. My RES don't hibernate since I don't really want them to or know how to let them.. so in the winter they really stop eating but they are still active in their tanks. I love it because it's like a 3 month vacation that I don't need to feed them or clean them
But does anyone else have this problem of 2 males fighting? Usually it's just the small turtle being mean.. he doesn't tear the skin or anything. What I'm afraid of is if the larger RES retaliates like he's done in the past and torn the skin of the smaller RES. Luckily this hasn't happend yet but any ideas of what I can do (and also for the topic starter hehe)