Hi angel2011, As far as i know we can have 3 kula dhevatha(yours dad's, mom's, if married then your spouse's also).You can consult an astrologer too get it cleared, this is from my knowledege. Ishta devatha will be one which is dependent on you. If you like all gods then everyone is your ishta dhevatha.
Hi, If you are single, then your Father Kula deivam is your kula deivam (god worshiped by your grand pa), if got married, then your kula deivam will be changed to your husband (father in law side) kula deivam. Ista deivam is your favourite got, who ever you like. Magee.