Terns - Arctic or Common? (1 Viewer)

Hi All - I am struggling with some tern ID. These pictures were all taken in early August a few years ago in Northern Denmark (location: Skagen Beach).

I cannot find out if they are Arctic Terns (Sterna paradisaea) or Common Terns (Sterna hirundo)?

There are four birds in question:
Collage 1: The same bird seen from two slightly different angles
Collage 2: A Sandwich Tern (Sterna sandvicensis) has caought a fish and a smaller tern is looking at it. The smaller tern - what species is that?
Collage 3: The same Sandwich Tern is now being chased by another small tern. What species is it?
Collage 4: This small tern was sitting on the beach and I got these two pictures.

Any comments will be appreciated.

Best, Peter

The white secondries point to Arctic Tern as well as the shorter bill & short legs on the perched bird.

#1 - juvenile Arctic / Havterne
#2 - adult & juvenile Sandwich / Splitterne
#3 - juvenile Arctic
#4 - juvenile Arctic

Juvenile Common / Fjordterne differs in being browner toned above (greyer in Arctic), with a dark secondary bar (pale secondaries in Arctic).

Hi Parker and Nutcracker - thanks a lot! A great help
Best, Peter

PS. And Danish names as well Nutcracker - great service