VLAN Tunneling and DHCP Client

Hello

I have a small problem with a special configuration.
For a larger building, I can’t get any further with the current technology, and have now decided to use technology from Mikrotik.
The original Internet dial-up router (provided by the provider) must be retained.
I have connected a HAP¹ AC to this, which acts as a CAPSMAN manager, and other HAP² Lites are connected in series to it, which distribute the WLAN further. That’s working so far.
But now I have to integrate a DECT repeater into the existing structure.
This DECT repeater needs an address (it is itself a DHCP client) from the provider’s Internet router.

So I’m looking for a solution without weakening the firewall, so that I can use a tunnel / VLAN from another PORT on the Internet router to create another line to the DECT repeater.

Simplified:
The MAIN Mikrotik router (CAPSMAN manager) uses another ETHER interface to have another connection to the internet router, but this is then tunneled through to one of the CAPS clients where this DECT repeater is to be connected without the router taking an IP address for itself. And this can get an address directly from the internet router via this tunnel/VLAN. The bandwidth of this tunnel/VLAN would still have to be prioritized so that around 280 kbyte/s is always available for DECT telephony.

My question is how do I set this up? Or is there another option/suggested solution?

Thanks
Frank