Once or twice a week is pretty low. My hubby and I usually do the deed about 3 or 4 times day..and that's after 11 years of marriage and 3 kids. I think the bare minimum is once a day..could it be that you have other things going on your lives that distract you? Or it could be a medical problem? Whatever it is, it's really not fair to say what's normal because you may have stuff that get in the way, kwim?
I should mention that at some times of our marriage it was down to once a day or even 3 times a week.. May just be a dry spell.
Good luck!