Hi, and welcome.
I would say yes you may use these as an intercom between the 2 buildings.
For batteries new alkaline AA batteries would be the minimum size D-cells would be preferable. Remember, even thees leak proof batteries may leak, so protect against leaks.
Tho test the phones (one by one at start) you should connect batteries between the terminal bat+ and bat - strap (short) L1 and L2 and you should hear yourselves in the receiver when speaking close to the transmitter (microphone).
With the receiver on hook the ringer should ring when applying voltage between L1 and L2 (remove short from first test, and move battery from battery terminals and use that, or just use another battery.
When this is done you have to connect the 2 phones, (with known working ringers

) Put a strap between ex - and bat-, try to ring the other end. (most likely, the receiver has to be on hook on the called station, and probably on the calling station.)
Enclosed; a guess on how the wiring diagram may be, based on your pictures. Induction coil is the black cylideric thing in bottom of the phones, with 3 wires. (this is actually a transformer)
dsk