Help Urgently needed to help connect Google Nest Protects and Camera/Doorbell to TP Link Deco Networ

5 years ago we downsized from family home in Dublin Burbs to Totally renovated Artisan terraced house in Irishtown for our retirement as all the kids had flown the nest. It was a major opportunity to get a small modern dwelling near everything for our retirement as the the house was derelict and needed Toal rebuild. We chose Nest products, Learning thermostats, 7 Nest Protect smoke alarms ( Architects insistence on number) and 2 HQ Nest Cameras (Indoor & Outdoor HQ) And Nest Doorbell . These were connected to Apple AirPort Extreme Routers and worked perfectly for 5 years until we decided to upgrade the ageing Apple Routers with TP Link Deco X75 Mesh Network having been informed that the best reliable solution. Anyway to cut a long sad story short we have only managed to get 1 camera online and none of the Smoke alarms despite resetting them to factory defaults and reading all the help and as many forums as possible and having contacted both Google and TP Link help chats and getting zero useful help as to what the problem might be but many people seem to have similar problems and I have tried their fixes but none have worked for for me as I am not a Network expert , just a keen amateur photographer who has used computers for about 35 years but not qualified.. We changed the routers 4 months ago and everything else in the house is working perfectly. The Nest/Google monitoring contract id due for renewal in 10 days and we have to decide how to fixit or replace itbut this is a difficult option on a limited pension and with nearly 10,000 Google staff living and working nearby but with no way to connect to anyone without walking in to their Head Office in Barrow Street as they have no telephone contact numbers. I am willing to pay someone to help restore this service as it would be beyond our present Budget to replace. Somebody please help!