Because you also lose mobile phone signal power with antenna extension cables, you should not use them (the two outer antennas are mobile phones (LTE), the middle one GPS). It is better to place the router in a location where the mobile network is good and use a long network cable. This can also be used to supply the router with PoE so that no power supply unit is required at the router's location.
The router also has two WLAN antennas on the lower side. The positioning may not be so good for Wi-Fi reception. But you can also switch off the WLAN on the UMR and connect another WLAN access point in the living area.
I would rather do it this way, but in principle you can of course also place the LTE antennas with long cables. I don't know how much additional signal attenuation there is per metre of cable. It certainly depends on the quality of the cable.

Connections of the UMR Industrial: https://techspecs.ui.com/unifi...