In SpongeBob, we usually see Patrick with his parents, Herb and Margie, right? Well, I've got a theory! (and correct me if I'm wrong about it) but I think Patrick's real parents are Bunny and Cecil. They had Patrick, raised him until he was almost grown up, and then they had to give him up for adoption.
Herb and Margie then came into the picture and adopted Patrick when he was still a teenager. Now, it's a bit confusing because "The Patrick Star Show" seems like it's in a different world than the main SpongeBob series. In my theory, Patrick was actually born in a house shaped like a coffee pot in a place called Ukulele Bottom, and he even had an adopted sister named Squidina there. Later on, when Patrick is with his new parents, they purchase the well-known rock house in Bikini Bottom fir him. And one more thing, Patrick didn't meet his real sister, Sam, until after his first parents, Bunny and Cecil, had already given him up.