How can I convince my family that my mother in law should not be driving?

I do not trust my elderly mother-in-law to drive my children anymore, because she falls due to uncontrollable dizzy spells and blackouts, but my husband refuses to agree with me that she should not be allowed to drive them anymore. This is putting an incredible strain on our marriage! She needs to be in assisted living and not driving at all, but he wants to just wait until she falls and breaks her hip before doing anything. That way he doesn't feel guilty. His siblings are no help at all. We are bearing all of the burden. What are we supposed to do? We are stressed out and not sleeping. Help!