Looking for VoIP WiFi handset with call forwarding

Hi mates, thank you for your kind help and time,
I have a particular request, a restaurant which desires to have 2 cordless phones, one in the main room, the other in the office far away, a DECT will never work/be signal RF covered on both places, I would like also they have the chance to call each other and eventually forward the incoming call to the other.

Since the WiFi is well meshed everywhere, I'm thinking if there exist alreasy some VoIP handsets that could directly connect to WiFi, the base will work only as charger, I imagine one programmed as master will receive call and ringing as first, then transfer call to the second agter 40 seconds (on same LAN/WiFi), or manually transfer during the call, or call the other as an intercom, etc.
Such things do exist?
Are the wifi phones for some reasons not recoomended? For example to keep connected they may use lot of battery, or on movement the call can drop easly, etc.

A classic solution can be a Voip PABX/server able to manage all this features and 2 simple VoIP DECT, but it looks more expensive.
Thank you for suggestions!

hi, no help here? (