XB7 DHCP Pool and Ethernet Connection Issues

Hello, so, first off, I am not the primary account holder but, rather, my father and I have an agreement that I pay for our house and my parents pay for the utilities as they are living with me.  Nonetheless, for any technical support or WiFi issues, I (the son) am the most capable to fix things connection-wise.

Anyway, I have a system of switches and connections setup via Ethernet (1 primary and 4 intermediary) and I have two problems regarding them, though the wiring and everything does work.  

Firstly, the intermediary switches are unable to be connected to each other directly without the internet connection via Ethernet cutting off (I simply have a hub and spoke architecture for now as a result).  This doesn’t seem to be an issue with the company or the two models of switches that I obtained.  

Secondly, I tried to reset the upper end of the XB7 router from 10.0.0.253 to 10.0.0.189 as I wanted to reserve 10.0.0.192 to 10.0.0.253 for devices connected via Ethernet.  However, my current issue is that my devices are still all connecting to their old addresses, and since many of these devices are smart devices, I cannot change their IP addresses directly in their own interfaces.  I was thinking that the subnet mask may need to be changed from 24 bits to 25 bits and a technical support agent agreed, so we had a plan of changing the IP address and the subnet mask to fit this.  Of course, these changes never actually showed up on our XB7 router (which may be a good thing in hindsight).  So I’m wondering if changing the subnet mask along with the DHCP pool may be the option that I’m looking for or if other options are available to fulfill what I’m trying to do.

Any input would be appreciated, so thank you.