Telephone with answerphone and 4 handsets (Wetherby LS22)

We have just had Fibre Broadband connected to our house and our phones are not compatible with the new system. I don't know whether anyone can make use BT Freelance system. It has an answer phone and four handsets. It also has an intercom system so that you can call people in another room. It worked very well when plugged into the traditional telephone socket but does not work from our router. This is a link to the manual if you need further details.

https://www.bt.com/content/dam/bt/help/legacy-ug/phones/BT%20Freelance%20XT...