Five/four prot paladins?

[EaTCarbS]

Instead of going protection on any of them, would it be possible having 4 retribution sharing aggro + a healer?

You may as well spec one prot. He will be able to take damage better than a ret and put less stress on heals.

[Ughmahedhurtz]

You may as well spec one prot. He will be able to take damage better than a ret and put less stress on heals.

This. To be more precise, bouncing aggro is tricky and prone to error. Furthermore, one good prot tank can absorb more effective damage than 4 rets combined. Eventually, the content you're doing will outstrip your healer's ability to keep up. That threshold is a LOT higher with a prot tank than with rets.