I have checked the RV016 manual and I like this router a lot for its features.
Let me clarify that the group of PCs that you will have a rule to go through WAN1 or WAN2 can't be load balanced as the rules will overwrite the load balancing mode.
- Go to "System Managemen" -> "Multi-WAN"
- Select the WAN you need and click edit.
- on the button you will find "Protocol Bindings"
- for the service select "All Traffic"
- in source IP type the range of IP addresses from - to , if its only one address type the same IP in both text boxes.
- in destination IP type 0.0.0.0 in both text boxes.
- check enable then add
Do this for other WANs
note that If IP addresses that does not match with any rules will be load balanced between all WANs configured.
for NAT rules can you explain more what exactly you need to do ?