The Spirit Realm

On a ranger - I've occasionally 2-boxed a ranger, though not much since I don't really like 2 boxing. If the ranger is well enough geared, they're not bad tanks. Obviously not as good as a knight or warrior, but similar to a monk. At lower levels, ranger tanking is fine, at higher levels, the gear needs more work. I used to duo with a ranger tanking, and that worked well. The ranger needs more healing than a knight partner, but the mobs are dead quicker so it evens out.

Alternatively, you could root/rot with the shaman and have autofire on with the ranger. As long as you have the archery AAs and a decent bow, that's not a bad way of doing things, and less effort on the ranger. I used to do it that way a bit, but that's partly because I wasn't very good at 2-boxing (I didn't like not playing the shaman at 100%) so I treated the ranger as a bit of extra ranged dps.

Paladin/Shaman has to be one of the most powerful combinations out there. I box Pally/Shaman and it's a pretty darn good combination. You get the buffs from the Paladin that all stack with Shaman. You get the Paladins ability to stun, not to mention the slay undead capabilities at later levels. The Paladin can tank well on most content. You also get his 90% rez capabilities and invis to undead capabilities if going after that content.

I always recommend Pally/Shaman as a duo.

A ranger could tank older content fairly well, up to at least level 70 given modern gear, I'd say. So it depends how far you want to take it. If you're heading for level 80 and SoF content, then I'd say a ranger is probably not your best bet as a tank.

As for summoning mobs, again, depends on the content. Anything a shaman can solo, a ranger can do passive dps on, naturally. That's all I used it for, but again, if you want to do the most recent content, that might not be the best bet. Though there are quite a few spots a shaman can solo even so, so if you want to make it work, you can.