I want to fly to Costa Rica San Jose, Club, using my airmiles. I have enough for my return ticket. I wanted to use my companion voucher for my husband but have been told that I can only use it for BA flights. The leg from Miami to San Jose CR is with American Airways. Can we use the companion voucher for the first leg and pay for the 2nd leg.

My other question is, if we both just fly to Miami, and then get our own flights to Liberia (CR) (which is actually the airport we want to go to but are not being given the choice on the BA website) do we have to collect our luggage ourselves in Miami and go through immigration, or will the luggage be transferred to the next flight even though we have booked it separate from the BA part of the trip ?
Any help is appreciated.