Too many cars

Why are you living with them? You should probably focus on your own life in all honesty.

You could talk to them about it but it's their call so I'd just not bother about it unless it's an inconvenience rather than just a quibble.

It is kind of inconvenience because its reducing space on our driveway and its not environmental friendly

Then talk to them about it.
Bear in mind that having more cars doesn't create more emissions than using a smaller number of cars more so that argument isn't terribly well founded.

My boyfriends dad just buys cars, I came home from work and saw a new car on the driveway and my boyfriend tells me it's his dad's. We don't need this many cars, my boyfriend has a car, his mum has a car, his dad already has a car in the garage we don't need this many cars it's ridiculous. I live with them and when I go to work there just so many cars on the drive and it's unnecessary. I don't understand the reasoning behind this. Only 3 of them drive, my bf, his mum and dad drive but they have 4 cars? My boyfriends little brother lives with us but he's 11 so too young to drive. Its just unnecessary.

If it's his house and he is buying the cars with his own money, it's up to him, to be honest.

He might be planning to sell at least one of them but doesn't feel that he needs to discuss this with you.

If it's something which genuinely bugs you, perhaps talk to your boyfriend about the two of you getting your own flat when things get back to normal.