Part 2: Part 1. Then replay Kleer room onwards with knife from save point. Need just remaining half of map. The best way to tackle that green aldurian reptloid towards valley end is after killing bulls kamis near hole, hide near valley hole where you kill scorpion and stay on right side of cliff hiding till you reach corner of rope bridge. then jump out duck behind the tree. that shields you from his green fireballs lot. Then jump out quickly kill it circling him. Allow kami to hit you no issue. Then just run past mini lava golems from side that should help you avoid kleers. Just watch out for rocketeer rockets he is only threat but i managed to dodge all without taking any more hits in a single sprint just jump in water knife 2 fishes as you reach exit platform and done. For the last sprint after killing aldurian reploid you need at least 35-50 HP to get in and survive map end. I had 52 no trouble. So save up and dash.

Part 1. I finished all 3 hard grinds today. Killing and using Guns is useless all 3. I used knife only to kill 7 in the room after entering temple past flamethrower. You can enter kill scorpion fast and come out before door closes. Then enter till halfway and come out again. That way enemies break out but you are safe outside. Now open door lure them out duck by door side frame and take them out with knife without losing HP. Same way wait outside door and lure trap Pumpkin outside room. So till you reach Kleer pit with double barrel gun, you are good to go having sued only knife. From that point routes diverge. Finish Who needs kills using guide video in your write up using 4 rocket jumps to avoid anymore fighting for Killing is Useless. .

I finished cooperative first encounter last map and it unlocked achievement. Finished same TSE completed map it didn't unlock.

I've done them in SP, so I cannot confirm.

Too Serious for weapons
Complete a level in The Second Encounter using only the knife on at least normal difficulty.

Guns are seriously useless
Finish 2 levels in The Second Encounter using only the knife in at least normal difficulty.

Who needs kills, anyway?
Kill less than 8 enemies on the first level of The Second Encounter in at least normal difficulty.

That all you got?
Finish the first level of The Second Encounter taking no damage in at least normal difficulty.

Jumping is overrated
Finish the first level of The Second Encounter without jumping in at least normal difficulty.

can these be done on coop?

You can get Afterlife achievement in splitscreen using minetrap letting it kill both of you so stand real close and use it on your alt player.

Christmas 2014 could be obtained in COOP but last time I played, only the host could get the achievement and the other players wouldn't get it.

EDIT: Well Bouncy Rock unlocked in Coop waiting stage itself without clicking F3 blowing the trees. LOL!
So now Christmas 2014 Achievement can be done in coop?

Yes you could do "Marsh Hopper" like that, I've done "Sam I Am" like that by loading a quicksave. I don't know about unlimited ammo, I haven't tried so I cannot answer that one. I haven't used any rocket jumps so I don't know how it would work. But if you don't kill any enemies you should be fine with the knife achievement. Yes all single/coop campaign achievements can be done in Tourist difficulty.

or Marsh hopper with chainsaw in Pitt can be done tourist mode and use quicksave relaods? in some of those achievements like not losing hp in normal etc can you use unlimited ammo? Also where you must use only knife to kill, can one use rocket jumps as rocket is not used in killing or its strictly must not use any other weapon? Can all campaign runs single coop bright island be done tourist mode?