OVPN devices and SOHO devices are in different IP subnets. So it’s all about routing and firewalling. You need to configure OVPN to instruct peers to pass traffic for SOHO subnet via OVPN tunnel (if OVPN doesn’t request from clients to use tunnel as default route). Then configure firewalling on router to allow that traffic. And configure firewalling on SOHO devices to allow traffic from OVPN subnet.
There’s nothing to be done on L2 (VLAN) configuration at all.
If you want OVPN clients to use IP addresses from SOHO pool (so that SOHO LAN devices consider OVPN clients to be in same LAN), then you’ll have to assign OVPN pool some addresses from SOHO subnet. And enable proxy ARP on relevant interfaces (OVPN, SOHO) so that router will answer to ARP requests from both sides.