Wedding invitations in British English
The British authority on such matters is Debrett's. Recommendations on the wording for wedding invitations are given here.
Afterwards would definitely be the preferred word in my experience.
Inviting somebody to a marriage does seem to imply that they are going to be houseguests for a good few years! It is regularly used though.
If the couple are personally inviting the guests then I would suggest “our wedding”. If one or both sets of parents are issuing the invitations then either is usable but I have normally seen “the marriage of…”.
(I’m English by the way)