Do folks have insurance cover for both riders ?
IANAL, but I think this question is worth being asked only if the two crew members live in two different households. Otherwise, both members are normally covered by the same insurance.
Only really if you were both in an accident and both needed to make a claim against a third party.
If you drive your car with your partner/children on the passenger seat, you have an accident, both of you are injured, you do not need to have two separate insurances. Why would it be different on a tandem?
A