I agree with Tweed. Pet tanks aren't going to hold up as tanks against more difficult mobs. Outside they should be fine and lower dungeons they could be doable but tanks in EQ2 have a lot of tools to mitigate damage that pets don't get. Even real tanks can take huge damage spikes ...pets get turned into confetti.

And you will be trading off a lot trying to keep a pet up. Healers don't just heal in EQ2, the game is tuned with the expectation that healers will also cure and debuff at all times and DPS when possible. Trying to keep up a pet will kill any debuff cycles that your healers should be performing. Using the parent class of the pet to control the pet via thier pet heals/mits will interfere with the DPS they should be putting out. You may be able to juggle agro with agro transferrance spells, but again, that's more stuff to do that detracts your attention from actually DPSing. And unlike WoW, agro on tanks is as much about the DPS the tank puts out as it is about taunts, so you will be losing the DPS that a proper tank brings. You will probably find that after a certain point, you can't transfer enough agro to keep a mob off your toons and can't kill fast enough to keep your toons from running out of power.

All healers have AOE heals. The way healing works is not about direct healing for the most part. The main line of defense is mitigating damage, via wards, reactive heals or HoTs, depending on class, and curing. Basically a healer prevents damage first, restores chunks of health second.

The other way EQ2 is different from WoW is stacking is futile. Buffs from the same class won't stack. The game is designed for other classes to compliment each other, it's expected that you go into instances with certain types of buffs. You want to cover the widest spectrum of buffs and that you can in a group. With multiboxing, you get the benefit of focusing your buffs. For example, my current group is SK, Temp, Defiler, Warlock, Illy and Troub. Defiler gives me noxious debuffs, which helps my husband's SK and my warlock since they do noxioous damage. It's a caster heavy group, so my troub and lock both provide lots of power replenishment. My illy provides buffs to melee attack for my troub and SK. And so on. You want to pick the classes that will give the most bang for the buck for your playstyle.

It's kind of overwhelming at first, but you just have to break it down into steps. For me it was starting from the top down. My husband is playing A tank. Therefore the kind of damage I can expect will require B healer{s}. I want {caster or melee} DPS which makes my group {caster or melee/AOE heavy or single target focused}, so I should have C for utility. From there you can refine it down to specific classes and chose them based on what they bring to the table for general de/buffs and specialty de/buffs.

There's a ton of nice info in the Wiki that will be very helpful.