sharing a well

Two homes share one well-on my property.
One holding tank is in the second property.
My line is before the holding tank.
Can I put in my own holding tank?

Sure you can, but chances are it won't help anything. The water is still coming from the well and some from their tank. Tanks hold very small amounts of water and once emptied, it's again up to the pump to keep up.

bob...

tank

Yes, assuming the piping is done properly, but all it will amount to is increasing the total water drawdown before the pump starts. You will gain a slight amount of pressure because of the shorter pipe from the tank to your faucet, but few other benefits.