
It appears your best bet will be to stick with Chase and UR points. You are looking for bargain international fares for a number of people. More often than not paying with URs via the Chase travel portal with a CSR account will be a better play than transferring the URs to an airline for seats in coach. The CSR will make your points more valuable in the portal at 1.5 vs 1.25. When the time comes to pull the trigger, if you find it would be less points for an award seat on United you can transfer the points 1;1 instantly. In your situation, I would not be getting the United card. My suggestion would be to go for an MDD on the CSP/CSR. Then have P2 go for an MDD on the CSP/CSR. I'd look at getting a CIC, CFF and CFU.
The Chase family of cards allows you to earn more URs at a faster rate via bonus categories. The Freedom Flex has rotating 5x categories for up to $1500 in spend each quarter. DH and I each have 3 Freedom cards for the express purpose of maxing out quarterly bonus categories. That amounts to 60k UR a year with no AF, no hard pull.
A CIC will give you 5x at office supply stores (up to $25K per year spend) which sell gift cards for 3rd party merchants which can get you close to 5x on most of your shopping. Staples and OD/OM often have sales that eliminate the activation fee on VGC and MCGCs which can get you even closer to 5x on all spend. When you are shopping online, you can find many merchants through the Chase UR shopping portal and beef up your URs by shopping through there. We each have the old Ink Plus which is like the CIC for 5x at office supply stores but lets you spend $50k a year in bonus categories. This is the work horse of our UR family of cards.
Hope this helps