2000 Ford Fairmont Long Term Parking of the car

I park my car in the garage for 3-6 months without driving it. The problem is the battery goes "dead" and I have to get the battery replaced. Even after replacing the battery, it goes "flat" after 2 months even if its started once a week.

My questions are:-
Q1. Is it ok to disconnect the battery from the car and leave it stationary until I come back from overseas.

Q2. What would be the damage to the car engine if I do the above.

Q3. Could you suggest a better solution if there is one in relation to long-term parking and battery draining.

Thanks.