Is intellectual disabilities something that run in families?

Yes: It most certain can. Obviously intellectual ability is a genetic trait, but sometimes a genetic disorder like fragile x or another mutation is transferred from parent to child. Some disabilities, especially metabolic disorders that lead to autism, are. Of course, if parents are intellectually challenged, stimulation is low, hurting child development and their iq. It's still nature vs. Nurture.

Yes.: Familial, inherited factors are actually the most common cause for intellectual disabilities.

Some; in part: Iq is ~60% heritable. So the probability a child's iq will be near the mean of his/her parents' is higher than that it won't. Severe conditions that affect the brain's development can be inherited, yet often do not show themselves in prior generations. Yet other conditions do run in families, and are seen in collateral relationships. One must know the details. Familial "risk", not "certainty".