Why do you want to complicste simple matter. Make 4 sys-vpn qubes, make source of it’s network a sys-firewall, and connect your app-vm to sys-vpn of your choice.
Somteime I use 6 different sys-vpn's simultanesly.
This is not Qubes specific - you could look to see how Network Manager
might deal with this.
The main issues you will have to deal with are handling DNS resolution
across different VPNs, and ensuring that there are no IP conflicts. This
is not impossible, but it is so much easier to set up separate VPN
qubes, as @KitsuneNoBaka says.
If you want one qube to access two VPNs at the same time, you’ll have
no option but to configure multiple connections embodied in a single
netvm.
I never presume to speak for the Qubes team.
When I comment in the Forum I speak for myself.