- Arturo y sus abuelos se ven una vez al mes.

Although it only tells us that "una vez al mes" (they are seen once a month) I have assumed that it is conjugated in the present indicative.
Remember that in reciprocal verbs only plural pronouns should be used.
- "To we" ⇝ "nos"
- "To you" ⇝ "os"
- "To they" ⇝ "se"