Should I power up all Lapras and Snorlax?

Do you have the candy?

Lapras and Snorlax are always worth powering up if they're good (which yours are) and you have the candy to do so.

The problem is the candy is rare so most people can't afford to loosely power up 3 or 4. They need to pick one, the BEST one, and only power that one.

If you can max out 3, why not? Or at minimum max out the best 2, and you still have enough to max out a new one if you get an even better one.

Assuming you're not swimming in Lapras and Snorlax candy, I would suggest going for the following movesets:
Lapras defense: Ice Shard + Ice Beam
Lapras offence: Frost Breath + Ice Beam or Blizzard

Snorlax defense: Zen Headbutt + Hyperbeam or Body Slam

I'd say if you need both attackers and defenders, power up a defensive Snorlax (higher potential CP) and an offensive Lapras (great for dragonites and in general use, and will double as a great defender when necessary as Frost Breath Lapras is still a solid defender).

Matter of personal preference. I don't think it's necessarily wrong to power up all of them (assuming you would have the required candy), some would argue that only power up ones with A or B movesets or you can only power up good movesets with strong IV's. There's no right answer here to be honest.

For me, I only power up good movesets with good IV's.

It depends on what you are looking for.
Do you want attackers? Defenders?
Do you want both?

Forget the snorlax with 64% IV,you will regret it if you power him up.

For the others snorlax and lapras, it really depends on their movesets and what you are expecting from them...

And don't Forget that there are other pokemons.
Maybe you want to power up a couple of dragonites, vaporeons, arcanine, etc.
It costs a lot of stardust in the end so make a choice for 1 or 2 snorlax/lapras and don't power up all of the one you hatch/catch.

i think this is the pokemon go equivalent of thirdworld problems. Im level 26 and haven't so much as seen a snorlax in the wild.