My husband was found in possession of cannabis several months ago he was arrested and released, a garda has asked him to come to the station to be charged, does he have to go or can he just wait for a summons?
If matters have gone this far it is probably a matter of logistical convenience i.e. come to us or we will come to you.
Going to the station avoids a home visit !
If AGS want to interview OP's husband again that should be under caution and with a solicitor present.
A summons would generally only be issued if he is being summoned to attend a court hearing to answer a charge.
From what you have said so-far, no charges have being brought yet, but that may well be about to change.