I need a Network design to manage smart home devices across two networks

Question

I have a planned design but I need opinions and comments.I am not a professional. My family has two apartments (Apt A, Apt B), each with its own ISP modem (300 Mbps) and WI-FI 6 tri-band router. Each apartment has a number of smart devices. I would like to manage all the devices from Apt A. Some venders have apps that scan the local network for all of their devices so I want to scan Apt A as one local network. Apt B has three 4k+ TV that use 25 to 50 Mbps each, so I want that load to stay only on the Apt B ISP. Both networks have devices that need a static IP. I have a WI-FI 5 dual band wireless router (Router C)that I can place where it can see the Apt B router on 5gHz ac. It will connect to Apt A router using 1-gigabyte ethernet. My design is to make Apt B a subnet of Apt A.

1. set Apt B router to IP 192.168.1.128, Netmask 255.255.255.8, DHCP Range 192.168.1.136 to 192.168.1.254, and SSID Apt-B.
2. set Router C to IP 192.168.1.4, Netmask 255.255.255.0, DHCP Off, and SSID Apt-B.
3. set Apt A router to IP 192.168.1.1, Netmask 255.255.255.0, DHCP Range 192.168.1.8 to 192.168.1.127, Rule (192.168.1.128 to 192.168.1.254) -> 192.168.1.4, and SSID Apt-A.

Comments appreciated.