After reading your post, I decided to give Double Battle Factory a try too!
I lost at 18 with 8 swaps. Of all the things I could have lost to in the factory, I lost to the good old freeze hax. :( I would have been happier if I lost because of a lack of good pokemon to pick from or something.
Ah well, here's a medium length summary:
Oh, and I didn't look up the pokemon database (if you're wondering why I don't even remember all the moves my pokemon had).
Streak 1 - 7:
I started with:
Lead 1: Yanmega(Speed Boost with DETECT, Signal Beam, Air Cutter, and something I never used)
Lead 2: Quagsire(Earthquake, Aqua Tail, Brick Break, and something I never used)
Had different things for 3rd pokemon... don't remember anymore. I just remember most of the time it was Cradily.
Strategy should be ridiculously obvious. Quagsire EQs while Yanmega attacks or Detect if I suspect it's going to be attacked.
Had a couple close calls, just because I didn't really care about losing with the low streak anyway.
Streak 8 - 14:
I just had random things. I started with:
Lead 1: Snorlax (punches and chesto rest)
Lead 2: Infernape (Blaze Kick, Shadow Claw, Thunderpunch, Gunk Shot)
3rd pokemon: I don't remember, but after first battle I got a DD Gyarados with iron head.
There wasn't much strategy to be had with this streak. I just tried to switch whenever I thought something might be useful, but I think in the end I only swapped like twice. I had Espeon (Psychic, Charm, Attract, Swift) as my lead with Infernape for at least 3 of the 7 battles. Charm was surprisingly useful.
Streak 15 - 18:
I had the best team so far, but yah, that's usually when I lose.
Lead 1: Salamence (@Wise Glasses with Draco Meteor, Hydro Pump, Flamethrower, Ominous Wind that I never used)
Lead 2: Blissey (@ Bright Powder <that never worked> with Calm Mind, Boltbeamthrower)
3rd pokemon was Magezone (@ forgot with Charge Beam, Twave, Flash Cannon, Magnet Rise)
After battle 17, I swapped Blissey out for the Choice Scarf Tyranitar (punches + aerial ace), because I figured Tyranitar is a pretty good special wall, and... more importantly I thought having a physical attacker might be a good idea.
Battle 19 Summary:
I was facing Starmie, Dewgong, Skarmory. I thought my Ttar outspeeds Starmie (yah, I looked it up just now, my bad. 180 speed for Ttar, 183 for Starmie), but nope, Starmie Blizzard KOs Salamence and freezes Ttar for 7 turns. Magnezone put up a good fight, but got confused from Dewgong's Signal Beam.
I might try this again. This seems less annoying than Single Factory. I've always liked Double more though.