missing my cats

when we moved to the city, there is this cat who kept on following us until we sorta adopted her. she grew up in the building where we moved and later on i found out that she moves from one owner to another from time to time, like a migrant cat. but then, people dont really like her coz she steals food from the table and she has this attitude problem so the corridor is her home. but then, since we moved, she spent a lot of time with us, pleasing us so that she'll become part of the family. but whenever it's mating season, she disappears and then comes back pregnant. the first time she gave birth in our house, all her kitties died coz they are premature and it was a rainy season. i felt so sad then. the second time was successful though. we were excited, they were 3 cute kitties, one looks just like her mom, a british white and tortoiseshell short hair (female) , the two were odd-eyed british white short hair (male and female)..i somehow spoiled them and pampered them, treating them as if they're my children..i've taken lots of pictures of them too, from birth til last week..four months passed, another set of kitties. my parents want me to give away the three new ones coz 4  cats are already a handful. now the first set of kitties were seven-month-old ones, the second were 4-month-olds..weeks ago, my 7 month old queen kitties were acting weird..i found out that they are ready for mating and oh no i havent spayed them yet. they never been out the house coz we live in the 4th floor of the building. and just three days ago, the tortoiseshell one disappeared. i was really worried that i asked around the building if anyone saw her but no one did. then this morning, the male white shortie was taking a nap on my window sill, one second he's there, then another sec, he's already missing! i searched for him on the ground floor but i didnt find him. is it really normal for cats to go out their home on mating season? well, im so worried about them. my dad has just arrived and he's on a rage when he found out about it coz this male white cat is his fave pet. awwww sadness :( i just hope they're safe and they'll be able to find their way back home.