Control room setup with 5 remote workers

Hi Everyone, I am looking for advice on the best setup for an office to be used as a base station in the centre of an estate, used to communicate with 5 remote game keepers. Range is upto 4Km of undulating terrain mainly fields with patches of woods scattered around.

I have 5 years of signals experience in the UK military mostly with analogue VHF HF and UHF technology but havent touched it for 20 years so not upto speed with the latest products. My experience is mostly on old Clansman kit