Learn English – In or at the department of English and American Studies

I have to admit I haven't consulted any sources, but here is what I'd say is "correct":

• On Saturdays, her sister Ann usually comes to stay with Mary for the weekend.

and

• What are you going to do for the weekend?
• What are you going to do over the weekend?

and

• We are going to Paris for the weekend.
• We are going to Paris over the weekend.

"Weekend" would not normally be pluralized when preceeded by the word "the". For example:

• Are you going to stay here on weekends?

And finally, to address "at the weekend": this is often seen in British publications, but I've never seen the phrase "at the weekend" in American English.

When talking about people it's either "She is married to him" or "She married him". When talking about objects the preposition "with" is used: "This wine marries well with beef"

Note: the above is an oversimplification - marry "with" was certainly used in past literature. The following chart shows the relationship, married with is multiplied by 10 otherwise it just shows up as a line at the bottom. This also makes no attempt at separating things like "wine married to beef", which might explain, or not, the apparent increase of usage in the last 50 years