I have name changed for this post as I'm a bit embarrassed about the subject matter. Ive failed as a parent to my younger dd's, totally.
I have 4dc, a son of 14 who has autism/adhd, an 11 year old who is lovely, just stroppy and the two younger dd's.
Their behaviour is awful. The three year old is a nightmare, she is hyper, demanding,screamy, will not go to bed and stay there, clingy, will get herself out of the car seat when driving and launch herself at me or try and climb out the car window again when I'm driving, forcing to stop quickly obviously putting us all and other road users at risk, rude and irritable and obsessive. But brilliant at school 
She was a brilliant baby until she hit two and I've struggled with her ever since, her 6 year old sister pushes boundaries all the time and winds her sister up at times which makes it all worse.
I've tried sleep routines with the pair of them but both can scream for hours even when I go back to them or sit with them and then autistic ds gets aggressive with me because he can't stand the upset.
Ive tried everything, distraction, rewards, ignoring, everything. Nothin works.
And to top it all I caught the 6 year old playing with her bits, but she's doing it for ages and will not go to sleep till tennish and she's so tired. What do I do with that?I'm not so bothered about her doing that but its getting out of hand now.
I am such a shite mummy and they all know it. After 14 years ofparenting you would think I would have cracked it but the younger dd's are a completely different ball game to my elder two even ds with allhis problems.