Why is my dad is irresponsible when it comes to  a job , rent and bills ?

Ask your mother.  Some people weren't taught how to manage money.  Some people know how but their desire for things outweighs their common sense.  They are people who are incapable of delaying gratification.  They want something and they want it NOW no matter what. A person with bipolar disorder is often poor with money because their judgment suffers so they overspend.  And people with mental health problems find it difficult to get and keep jobs.  I'm assuming your father's inability to work isn't because of a physical problem since you didn't mention one.

It's a shame that your parents seem to be unable to sit down and discuss finances and give the family finances over to the person who can do the better job.  When my parents were first married, my father handled the family finances.  Unfortunately he did a lousy job but, fortunately, he knew it and acknowledged that my mother could do it better so early on in their marriage my mother took over the family finances and gave my father a weekly allowance.  Dad knew when the money was gone,it was gone and he wasn't getting any more until the following week.

I tend to overspend but I have always given priority to my bills first.  In the past I used charge cards but learned that lesson the hard way but, still, I always paid my bills on time.  Now if I don't have the cash for something, I don't buy it.

As long as your father doesn't realize, or care, that he is failing to provide properly for his family, nothing will change.  But I do think that your mother should seek advice as to how to handle this and then do what she needs to do to make changes.

No idea you will need to ask him