Arkham Horror was a Christmas present and my family is new to this game but so far we've enjoyed it.

This came up as we gamed.

If a player comes back to Arkham through the other world and closes the gate but doesn't have enough clue tokens to seal it can a player move into the location, to the gate, and seal it.

So another words can one person close it and another person seal it?

The short answer is no. Only the player/character who travels through an other world location and returns to Arkham is able to close and possibly seal a gate.

A thematic justification for this is that the player has only discovered how to close and seal the gate while traveling through that location.