Really this that's unlikely with berkeley homes -- so which development is that

Good to hear you will use an appropriate pair.

The RJ11 will be fine as it is a 6 position connector. If you find that hard to get hold of, you can use an RJ45 which is an 9 position version. An RJ11 connector will plug in to the centre of an RJ45.

Would still like to know if there is a master and filter elsewhere and if so, the master you have should be changed to a slave.