See in Karnataka there are two ways to by land either you are agriculturist then you can simple buy agriculture land upto the ceiling limit if non agriculturist then you have to buy land by provision of 79 A and 80 as amended in Karnatka land Reform Act under this any person who is non agriculturist having family income less than 25 lack can with permission from deputy commissioner can buy the agriculture land.
Now in your case in my advise you should apply for any agriculturist certificate from the revenue office as your father has agricultural inherited land from ancestors it can be shown he is involved in agriculture through land labourers and you are involved to as it is joint family.
As in case the certificate in worst scenerio is not granted seek permission from the deputy commissioner for buying agriculture land and have to give your returns of family that is your wife and yours showing you have family income less than 25 lakh the permission shall be granted. Also the agricultural land can be purchased only for intention to carry out agricultural activity.
Further check the ceiling limit according to the land you have got as the ceiling limit under Karnataka land ceiling act is for A class land 10 arces and for D class 54 Acers in best of my knowledge.
Also contact a local lawyer he shall prepare the required documents for the certificate.