@alisha-- You need to get your dad help. You should speak with his doctor. Laxative addiction can be very dangerous. I know, I suffered from it too. But it's possible to quit. It's challenging and it takes some time for the digestive system to start working normally again but it's not impossible.
Laxatives don't just cause dependency, they also rob the body of the nutrients and vitamins that we need to survive. It's an invitation for illness.
I think it all starts with the mind. If your dad can make the decision that he doesn't need laxatives anymore and if he can make the needed dietary and lifestyle changes, he can free himself from laxatives. There are even rehab groups for people who have laxative addiction. These can also be a great resource for people who need support and motivation to make it.