Lets come to conculsion first before answering your question about destination NAT
Destination NAT is always inbound traffic . When outside network users wants to access inside network resources it's (outside to inside)
Example : Assuming you have hosted a application in your internal network and the requirement is wants to access application from internet ...
As per you diagram and explanation I can see that both end users networks are using same network subnet 192.168 5.0/24, in the case source and destination ip will be belong to same subnet ips will get conflict in this case to overcome this issue . Please use different ip pool subnet for Source natting purpose from traffic iniation side .
Assuming right side ...
You can't have two separate networks with the same subnet. The best solution is to readdress one of them.
Other possible solutions, such as using NAT or some type of layer 2 tunneling, are more complicated and subject to errors than readdressing.
Assuming you want use VLAN 3 & VLAN 4 as your LAN network and want to configure pat natting for internet access, and assuming VLAN 1 is used for DMZ network for hosting an application which needs static NAT.
Configuration of subinterface in router. For example in router subinterface configuration:
Encapsulation dot1Q 3
Ip address 192.168.2.1 ...