- A: We visit my parents every week since we bought the car.
- B: We have visited my parents every week since we bought the car.
- C: We've been visiting my parents every week since we bought the car.
All three above are correct. A uses the present simple („we visit“) to
show it's a regular occurrence. B uses the present perfect to describe an
action that began at some point in the past and continues up to the time of
speaking. C uses the present perfect continuous to focus on the continuing
nature of the activity.
So the choice of tense in the first clause depends on which meaning the
speaker wants to focus on.