The couple is going to purchase the house? Or the couple are going to purchase the house? Even after all my years of editing, I can still get tripped up trying to make verbs agree with collective nouns like “couple,” “team” and “majority.”
Collective nouns are singular in form, “a team,” but refer to a group of two or more people or things. In other words, they’re singular and plural at the same time. And since verbs are supposed to agree in number with their subjects — one cat is, two cats are — the roughly 200 collective nouns in our language cause a lot of confusion.