I don’t think ‘couples counselling appointments’ refers to two appointments.
Additional punctuation would help:
I think we need to go to those ‘couples counselling’ appointments = I think we need to go to those counselling appointments that are intended for couples (two people).
The preposition depends on the context:
We might go on a Spring break (like ‘go on holiday’ - referring to the act of taking a holiday/Spring break)
We might go in Spring break (during Spring break we might go to a certain place.)
Hi!.. well the thing is that Im pretty sure the girl who wrote that didn’t mean that those appointment were for couple, instead I think she tried to use couple as “two” so they were two appointments… Would it be fine then “Hi, I think we need to go to that couple of appointments”?