Routing single source to multiple VPN based on destination

[thebatfink]

Hi, I am using Merlin on AC86U. I have 2 OpenVPN clients (Client 1 and 3).

I would like to setup something like:
Source 192.168.1.100
Destination 1.1.1.1 -> VPN Client 1
All other destinations -> VPN Client 3
DNS is forced to VPN Client 3
If Client 1 goes down 1.1.1.1 is not reachable
If Client 2 goes down all other traffic is not reachable

Someone said ipset can achieve this (not possible via GUI) but I have no experience with anything like that. I imagine my requirement is not too far fetched - does anyone have this set up already and could share the setup so I can base off that maybe?

Thanks!