How on earth do I keep my dog calm around my puppy?

[TreeMenDos]

Most of the time he is chill with her but when she plays with him he doesn't understand he is 5 x her size.

He bounds and jumps and play snaps but it's too much.

Shall I seperate them when he does this? Who do I remove?

What is to say it is too much for the pup and not that it just looks bad? Are they very different in breed sizes? How old is your adult dog? I would think if there is no aggression then they would work it out.
But if it is getting dangerous I'd remove the pup to the other side of a gate or crate. Can you distracted the older dog with some sit and treat training if s/he is getting too much?

They are both small breeds but the pups are tiny and he is heavy/stocky.

Several times he's jumped on her and she has yelped in pain. He gets completely focused on her and is relentless in snapping at her, he's caught her a few times and again she has yelped.

No tellings off. Just calmly separate them whenever you think it's getting too much. Tbh I don't think it does any harm for tiny pups and adult dogs to spend lots of time apart. There's plenty of time to build a relationship when the puppy's a bit older. Right now it's all about damage limitation.