You can run two pumps on one return if you have TEE them together, and have a check valve on each pump before the TEE.
That also works well with feed mode.
It is true that check valves are not very reliable!!!! But it does not really matter in this case.
Check valves get crud in them, and do not seal fully closed, so should not be relied on to eliminate a flood when pump fails.
But in this case, the check valve is really just to keep water from going out the other pump if one fails, so it does not matter if it leaks a bit.
Same for feed mode. A bit of a leak is no big deal.
But ALWAYS have a siphon break of some sort as backup.