Having two stacks is actually helpful in PvP. It makes it harder to cleave you. More like 3 "stacks" since your warriors would be stacked chasing targets and I tab between the two paladins, positioning them between heals or kiting when one starts taking damage. No matter what your group composition is, if you pick a fight with 20 players you're going to lose but warriors and paladins have more survivability and ways to avoid CC than most.

In large scale fights you just have to play conservatively. Pick off players that get separated and protect your clothies from rogues, etc. Once the enemy starts getting pushed back you can charge in and go ham.