Passive bonus to Paladin does not apply when active: base level 10 will apply +5% to Paladin when inactive, and +10% to Paladin and allies within radius when active.
Drinking multiple potions at once increases duration for which bonus is applied, but not bonus itself. Each potion has 30 second duration, so bonus will apply for 120 (30*4) seconds (2 minutes) to a player or hireling that drinks four of them.