Once you have met the minimum-spend requirements and thereafter received the sign-up bonus(es) on either or both of those cards, you would then have the sign-up bonus's dollar equivalent available on each card individually. That value cannot be combined in one purchase. However, you could use the points to buy one roundtrip ticket and perhaps one or two hotel nights with each card individually. There is no necessity that your airline ticket and your spouse's airline ticket be purchased in a single transaction.

Of course, the money you spend to meet the minimum-spend requirement would also earn points, so it's possible that you would have enough points for two tickets with just one card. Unfortunately, nobody knows what the price of those tickets will be once you have received the sign-up bonus.

However, unless this is the only trip you plan to take in the next twelve months, you could also buy both airline tickets as soon as you get a new card -- using the ticket cost towards meeting the minimum-spend requirement -- and then use the bonus points you earn subsequently; maybe even to pay for some hotel nights if your Hilton HHonors points are insufficient to cover all nights of your upcoming stay.