Weak Wifi with Range Extener

I know this is an old topic but nobody seems to have an answer that fits my problem. The Video and audio from my Doorbell 2 is choppy and keeps freezing. I put this down to a weak signal at the front door which is one floor down and at the other side of the building. So have bought a range extender - two in fact both of which were plugged in mid-way between the router and the Ring Doorbell. I follow the setup process to the letter and have no problem connecting to my Sky Wifi, but when I come to switch over to the network extender, nothing further happens, it just keeps searching on an unsecure network. The Wifi signal at the front door is weaker than if I just leave it on my normal network and Im just left in limbo. This is the second Wifi Extender I have tried, this one cost £50 as I though the first one may have just been too cheap. What am I doing wrong and do I need to do because Im not very tech savvy and cant figure out what the problem is.