It all depends how you're going to edit it.
You don't need the mixer if you want to keep it simple, just feed mics 1 & 2 into one camcorder, mics 2 & 3 into another (I'd suggest the two camcorders on sticks) and sort it all out in post.
If that's not an option then you need someone who can "ride" the mic levels (not as easy as it sounds) such that the mics not in use are turned down, otherwise you risk getting a lot of ambient sounds in the mix. By mixing live if you cock-up, you're stuck with it.
The mixer will have outputs (left and right) which you simply connect to your camcorder. Make sure that your camcorder is set for "line" input and I would suggest keeping it in 2 x mono with one track 6dB lower than the other to cover any "oops" moments. Digital video can deal with low sound a lot better than it handles over-modulation. Keep any limiters switched on and auto-gain switched off.
Failing that... My daily rates are very reasonable
The Behringer on ebay is a good price, I think I'll bid for it myself! ... (Only kidding)