It does not cost anything to join a frequent flyer program, and you assume no obligations by doing so. I suggest that both of you join the programs offered by American, Delta and United at this time. It will, however, be to your advantage to concentrate your travel on a single airline to the extent that this is possible.

The credit card is a different matter. If you wish to concentrate on AA, there is a credit card offer available with 30,000 or 40,000 bonus miles if certain conditions are fulfilled (see the separate thread for details and up-to-date information). I obtained such a crad last fall (no annual fee for the first year). I received 30,000 miles when I charged a total of $750 to the card, and will receive an additional 10,000 if I charge $5000 within the first six months. Purchase of AA tickets earn 2 miles per $, and I have a $100 credit if I buy a ticket on AA within a year of when the card was issued. You may not receive the same offer, but there should be something of this sort available to you.