Do you have rubber torsion axles, or regular leaf springs?
If you have leaf springs, you can jack under the axle tube where the spring shackles are.
If you have rubber torsion axles, you should have a subframe that the axles are mounted to. So, yes, you can jack between the wheels. But as the others have said, it is good to spread the load out. One suggested a 4x4, but I use a 2x2 heavy steel square tube, just because it is handier to carry in my tool box. But you can use whatever you have.
And especially if you don't have a subframe, I would never use a bottle jack without something to spread the load.