@AndyC7 

You can try moving Satellite E4 and Main Deco M4 farther away from each other. When E4 can't establish link to Main Deco, it'll connect to Satellite M4 instead.

You can try to artificially temporarily decrease signal strength from Main Deco, people had success by wrapping Main Deco unit with few layers of household aluminium foil. When Satellites connect the way you want, unwrap foil.

Note that this Satellites connection will only work until one of Deco units is restarted, and in your case it does not matter which one.

Some Deco models allow to configure how Satellites should connect to each other, but with what you have this is not an option. Firmware on M4 and E4 you have does not support that configuration setting.