Home network Spark Huawei with LAN & Apple devices in bridge mode

Hi guys

I'm also commenting in the Spark Sport streaming thread about difficulties I'm having streaming Spark Sport

@oblivian suggests I seek help here re. set up.

What I have is ...

A large 320sqm double story old villa, heavy beams, thick walls, 3-layered (false ceiling, ceiling & floor) between up/down

A CAT06 LAN spreading through the house from a hub in the basement

Spark fibre to the house, coming in via one of the wires to a LAN hub, because although we designed the whole thing for a wire coming in underground, Chorus in their infinite wisdom brought it in above ground to the top of the 2 storey house

So the fibre comes in to the attic, down through one of our LAN ethernet cables to the hub, out to the modem, then back to the hub

Modem is Spark Huawei standard issue, creating the ethenet lan and 2 x wifi networks (5G and not)

an early Apple airport express in a room downstairs far away from the Huawei, ethernet connected to the LAN, operating in bridge mode

a recent Apple airport extreme upstairs, ethernet connected to the LAN, operating in bridge mode

on one TV, an old Apple TV(3), ethernet connected

on a 2nd TV, a brand new ChromeCast Ultra, ethernet connected directly from a LAN port on the Huawei modem

A near-new Windows 10 PC and an elderly (2014'ish) Apple iMac both ethernet connected to the LAN

numerous phones, laptops, tablets, Amazon Echo and God knows what else all using the wifi network(s)

Problems ...

1) DCHP problems from time to time, especially the iMac and the laptops (interestingly, very rarely if ever affecting the near-new Dell PC) ... resolution 90% of the time is achieved by reset DCHP menu on the iMac (or switch wifi network on the other devices)

2) Nightmares getting the CCu to cast ... this is my major hassle. Typical use case is to use an iPad on the non-5G wifi network (because it's in the immediate vicinity of the Huawei modem, and that modem emanates a rubbish 5G wifi signal). The CCu nightmares are variously ... black screen ... picture but no sound ... total loss of control of where in the stream we are if we do anything other than play and leave it alone (so pause, fwd, rew takes the devices out of sync, at times by hours in a stream)

Oblivian (here) reckons I've almost certainly got a badly designed network. I could do with some advice. I am not a techy BTW, so in plain English please.

Many thanks, Don