When my grandpa was alive, he used to feed the rock doves on the balcony of his house. Now that he has passed away, there is a rock dove laying its eggs in a flower pot. I know that if he were still alive he would be happy.

When my grandpa was alive, he would feed the rock doves on the balcony of his house. Now that he passed away, a rock dove has built a nest in a flower pot. (or you could say "...there is a rock dove that has laid eggs in a flower pot") -- question for you: has the dove built the nest in one of your grandfather's pots? If so, that would be a nice detail to add: "...a rock dove has built a next in one of his flower pots." I know that if he were still alive he would be happy

When my grandpa was alive,he fed* the rock doves into his balcony of his house. Now that he passed away,there is a rock dove which is hatching the eggs into the flower jar. I know that if he was still alive he would be happy. * You have to use "fed" and not "has been feeding", because you said: "When my grandpa WAS alive" so if he WAS alive, you cannot use the term " has been feeding".