WiFi mesh with other broadband provider and Sky Q

[Quillion]

I switched from Sky Broadband Fibre to another provider as they could guarantee me superfast broadband (300mbps) when I was only getting 70mbps with Sky. I have a Sky Q box and 4 Sky minis. I have ethernet cables linking the router to the Q box and three of the mini boxes. The remaining mini is linked by WiFi. Attempting to create a mesh system throughout the house using the Sky boxes. Some of the rooms it works, I'm getting 200mbps but in the other two I'm getting under 10mbps. Currently have both 2.4 and 5mhz active. Can anyone suggest what I need to do to get this working? Thanks