I would like to configure that for the 4 prefix outbound, it would be round robin on these 2 peers and if one of the peer is down, all 4 prefixes would switch to the survival peer.
Keep you balance the way you are doing and you also can announce your /22 in both peers. If one peer goes down all traffic will be redirect to the other peer.
Upload is really easy. You need to create a ECMP route with check-gateway enabled. Just add both gateways in the same static route. The traffic will be share using round-robin every time source or destine address change. This way you can reach a good balance. Try it and tell us, ok?