First add the two address 10.0.0.3 and 10.0.0.4 to the output interface.
Create 2 rules for nat. one for each subnet. Specify the source address on each rule (192.168.1.0/24)
Don’t use action masquerade but use action=src-nat, and write in to-src-address the ip of the output interface (10.0.0.3)