Don't interfere with their marriage.
Don't interfere in their marriage.
Is the second sentence right? If yes, what's the difference? Are they ever/always interchangeable?
So the answer to your question is that the second sentence is right if you mean you should not interfere.
The first is right if you mean that you must not prevent the marriage.
Could you please give another example
to explain ''interfere in''
"Busybodies are people who interfere in things which do not concern them"
"He had no right to interfere in a dispute between gentlemen."
"It would be wrong to interfere in the affairs of the two cities."
Well, Brend, I've posted the thread, let's see if I got it right:
We shouldn't interfere in the upbringing of other couples' kids. (by giving opinions)
We shouldn't interfere with the upbringing of other couples' kids . (sounds strange, because preventing them to be raised is something stupid)