I don't want to babysit my siblings anymore.
Can you tell me why? For an outsider, there appears to be no good excuse.
It's a bad idea because I have a very demanding job and working for a company.
You should try and work something out with your mom. Pay for a babysitter and split the payment between you two?  So, you can focus at work.
Why should I have to pay for my younger siblings to be babysat?
Well, maybe you don't have to pay for it, but perhaps you can pitch in from time to time. All kids have to help their parents out sometimes.