Congrats. I'm doing London and Paris in May (will be proposing myself).

You should each get the Chase Ink Plus Business Card and the United MileagePlus Explorer Card. Each has a 50K and 30K Sign up Bonus respectively if you can meet the spend requirement ($12,000 total for both of you).

That may not be a problem if you will be spending money on a wedding in the near future.

With the spend, you will each get about 86K miles (To Europe is only 60K per person).