Can you have two medical insurance policies?

Yes, it helps enormously when a major medical expense is incurred, what one wont allow the other picks up.

It's just a decision you need to make whether the cost is worth it. Among the factors that have to be considered is that major medical policies nearly uniformily have "coordination of benefits provisions", which are intended to ensure that the insured does not get paid twice, and to clarify which of the policies is primary for a given expense.

Instead of two major medical policies, what one can consider is getting a supplemental policy that pays a fixed dollar amount per day while one is hospitalized or disabled irrespective of actual expenses incurred. In that way, the additional funds can be used by the insured to pay co-payments, deductibles, and other non-covered expenses. These kinds of policies are usually far less costly than major medical policies, although they also have far lower policy limits. They are typically available through work, although may be marketed directly as well.