1. Barclays is not very flexible, at least with the easy-to-use online redemptions. I could not redeem for train tickets in France because for whatever reason Thello is coded as a freight rail company, not a travel provider (maybe it has to do with the level of service provided on their overnight trains...) But with the $300 additional on the bonus and 10% of points redeemed back, my vote goes for Barclays.
2. Both programs score very well for any short-term devaluations, not so well if you have to buy very expensive tickets that could have been purchased with miles. I have redeemed points and miles from every major U.S. airline except Delta within the past year, and am consistently getting 2-3 cents per mile even for coach family (4) domestic tickets. For that reason, I would suggest one of you get an Arrival or Venture card, and the other get either a United card with 55K miles or two Southwest cards (if SW works for your travel plans) for a companion pass. You can get the SW cards later this month, before the 50K promotion ends Oct 30, and do the spending after the Dec statement posts so the points are earned and counted in 2014, and the CP would be good until the end of 2015.
3. You can only redeem against charges made on a specific account, so it is probably easiest to just get one card and add the other as an authorized user. Currently my wife has the Arrival card; the plan is that we run out the points and I get one before her fee comes due, so we never have to pay the annual fee.
4. I have no clue. I buy tickets, pray, and work with whatever happens. The unplanned things usually just add extra adventure
But welcome to Flyertalk!