I've been soloing my first paladin as retribution spec. In the early levels, with two of you, healing/damage mitigation really wouldn't be an issue if you were both ret specced. The mobs will be dead long before they can hurt you. When the mobs start getting tougher, well, by that point you'll have so much crowd control (repentance*2 for humanoids, hammer of justice*2 for anything, seal of justice) you should breeze through whole camps of mobs.
Of course, specializing one paladin as protection, and the other as holy or ret could be fun too. I haven't tried a prot build yet, but i've heard AoE grinding is a whole lotta fun!
A fun advantage of having a holy and a prot paladin is that you have the essentials of a good 5 man group already. Just grab 3 dps, and you can blast through any instance. With all the practice in your given healer/tank role, you'll be amazing the pick up members by how pro you are!