Tandem vs Triplet vs Quad -- Total team weight and riding preferences dictate the tire selection.
For "recreational" and "family" use, given the team weight of 360# plus another 60# for the triplet you might want to run 700 x 32mm or perhaps 700 x 35mm IF you're local roads are in bad shape or you think you might end up with some larger adults on the bike. The tire size will limit your selection to just a few of the more popular models:
- Avocet's FasGrip K's Duro Plus which is available in 32mm (and perhaps 35mm) widths.
- Panaracer's Pasela Kevlar which is also available in 32mm and 35mm widths.
However, if you're looking for something a bit sporty and you have good roads (I would think So. Fla would have fairly descent roads) you can certainly get away running 700x28mm tires. Models to consider would include:
- Avocet FasGrip K
- Panaracer Pasela K
- Continental Ultra Gatorskin
You'll want to experiment with tire pressures by running about 10 - 20 psi more than the min. recommended psi. on the sidewall, e.g., Avocet = 90psi, try them at 110 - 120psi. Pasela's = 105psi, try them at 125psi. Conti's = 120psi try them at 130psi.
There are certainly other tire options including Ritchey's Tom Slick's which have received decent reviews but the three I've listed seem to account for the ones that people who ride triplets & quads recommend when asked. You can find other candidates in addition to these at: http://www.sheldonbrown.com/harris/tires/622.html