Your brakes are basic Shimano Deore V-Brakes, not the best but more than adequate if they're set-up correctly.

The gizmo that controls both brakes is marketed by QBP under their Problem Solvers house brand of components and is called a "Cable Doubler". You can find instructions for it here: http://www.problemsolversbike.com/images/DoublerTwo.pdf.

Your rims are also pretty good, although the brake track could probably stand to be cleaned (see scrunge pads earlier in the thread).

Anyway, here's my diagnosis: You need to get rid of the doubler, add-back a left-hand front brake lever, get new housings and brake cables installed, get some fresh Shimano brake blocks (just make sure they're really 'fresh' and not old dried-out inventory) that are toe'd-in correctly and you'll want to make sure the Travel Agent V-Brake adapter are set up correctly.

As for the left hand / front brake lever, if you don't mind using the bar-end shifter for your front derailleur you can vastly improve your braking performance for not a lot of dough by picking up a fairly inexpensive ($21) pair of Tektro RL-520 V-brake compatible drop-bar brake levers. These are dead ringers for the very nice Cane Creek SCR-5V 'Ergo' drop bar levers for half the money. If you'd like to reconstitute your tandem to full STI dual control levers you can probably find a set of NOS 9 speed STI 105 or Ultegra triples on FleaBay for under $100. Newer versions will be more like $125-$150 slightly used. Either way will work but, frankly, the bar-end might be just as good and less of a hassle compared to an older set of STI triple levers that don't have the extra index points.

If you do all of those things yourself it won't cost all that much if you stick with bulk type cables/housing and $10 bar tape instead of the brand-name stuff. This is just basic maintenance and proper set-up. The V-brake adapter (that silver thing with the wheel) would NOT be needed if you put the Tektro RL520 lever on: they're designed to work with V-brakes, and that would be a good thing. You'll still need the one on the rear brake and you just need to be sure that the cable is routed correctly and the cam is aligned so that the opening is in the 2 O'Clock position. You can find the Travel Agent instructions here: http://www.problemsolversbike.com/im...agent_inst.pdf.

If you go with STI levers for both brakes, then the front would still need the V-brake adapter. As for brake squeal, I'm guessing that the rims were pretty messed up by the older brake pads and that your new pads weren't necessarily toe'd in correctly. Again, cleaning the brake track and doing a careful job of re-aligning a fresh set of brake blocks on the bike will give your brakes the bite that they should have. You can find V-brake pad adjustment tips about 1/2 way down this page: http://www.parktool.com/repair/readhowto.asp?id=21