Drop-In-Gateway use only IP range from secondary router?

Technical Support for Routers
1

I have turned off the DHCP server on my primary (non GL) router and enabled Drop-In-Gateway mode on my secondary router. I have two devices connected to the LAN ports of the primary router which have successfully accepted the secondary router as their gateway and DNS server.

So far, so good.

But those two devices still get IPs from the IP range of the primary router. I think this is the reason I cannot get those two devices to show up as Airplay receivers for my iphone which is connected by WiFi to the secondary router.

Is it possible to assign IP addresses from the IP range of the secondary router’s DHCP server to the two devices which are connected by cable to the primary router? How?

(The reason I can’t turn off routing entirely on the primary router and connect the two devices on the secondary router is that the secondary router does not have free ports).

2

In this context, I would be interested to know why IP addresses from this segment are still assigned even though the DHCP server on the main computer is switched off.
This is also the case for me and I don’t really understand it. Which DHCP is used for drop in?
(My main router is a Fritzbox)