Can you have two travel insurances at the one time?

In theory, yes.

However, the purpose of insurance is to make the insured whole in the event of a covered loss. Double recovery is not the goal. Therefore, collection from one policy will usually preclude recovery from the other.

Again, in theory, there may be circumstances whereby the policies cover different elements of the loss. For example, in the event of a cruise leaving from a distant location, one may cover the flight from home to the port of embarcation, and the other policy covers the cruise itself. If you are unable to go on the cruise, for reasons provided by the policies, in theory, you may be able to recover from both policies.