Can I skip minoxidil or finasteride dosage once or twice a week? Would it cause trouble for my hair?

While it won't actively hurt you hair, it will definitely lower the effectiveness of whichever medicine you choose to skip. In general missing occasionally won't have a significant impact, but missing a dose once a week will decrease their effectiveness. There's are reasons why they are meant to be used every single day, not every other day. If for some reason you can't take them every day, speak to your doctor about ways to work around this, if any.

Minoxidil is not as effective if doses are skipped. The hair follicle needs a constant reminder from minoxidil to grow. Skipping a dose once every month is not a problem, but once per week can lead to less effective outcomes. Finasteride is metabolized differently than minoxidil and functions differently. Skipping a dose every week is unlikely to jeopardize results.