I tried several times reviving my partner 3 times in the Amusement Park level on Easy, but at the end of the level the achievement never popped...
So I played on the Beach level, normal difficulty, doing exactly the same things and after the first attempt the achievement popped (at the end of the level).
The "strategy" is quite simple:
- choose Bud;
- let the enemy hit you until you are almost dead;
- switch to Terence with
and wait for Bud be finished (try to collect all the beer glasses dropped by the enemies, so Bud cannot recover his life);
- revive Bud with
- repeat twice more.