*A upgrades are not a particularly good reason to be choosing a ffp. Particularly when you want to upgrade partner airlines.

The operating airline chooses the upgradable buckets AFAIK And in most cases that requires an expensive full fare.

In other cases, you might be able to upgrade any Economy fare, but you will pay nearly the same number of miles as a J reward would cost in the first place. (i.e. TK)

So, you really need to decide which airline you want to be upgraded on, and then look at that airline's ffp to see how they deal with upgrades. There isn't going to be a generic "best for upgrades" but there might be an airline or two that works for you.

I would worry a whole lot more about getting redeemable miles out of the family travel. AC is a good one. Egyptair also works. You can merge Aegean balances for a fee or if you get elite status with them. There are possibly a few others...