My children won't respect anyone except their father

I have a son 11 and a daughter 8 and I have shared custody with their father.  I have them for the school year and him summers and alternating xmas.  My son has extreme anger issues with me and disrespect towards anyone of authority especially women.  It is like the world revolves around him and no one else matters. Everything that goes wrong for him is always someone else that is at fault. He always says I always tell him "NO" so he wants to live with his dad because he is able to do anything and gets anything he wants.   My ex has been very verbal about our previous issues and also has lied about alot of facts and I have tried to remain very hush hush.  He doesn't work, have a car, a house of his own (his moms) and hasn't paid support for over a year but they respect him more.  Both of my children feel as though I am being mean to him by making him pay me but again his family has given this info not me.  We just meet for the xmas swap and my kids were both raging angry because he got pulled over by the police and had a suspended license from default of c/s. So they want to go to court and live with him so they can help him and see him more. Again more money that I would have to spend to keep them with me.
This has been an issue for years and is getting worse and worse each time they see him.

I have a boyfriend of 3 years and living together for 1 1/2 and he can't do or say anything without them getting mad at him or just ignore what he says.  I have stepped in when I am home but I am not always around.  I work all the time to be able to afford our bills and fun things we do together.  So I need to figure out how to stop being the middle man for everyone and have everyone get along. I am exhausted everyday by this and tend to give in alot of the time because I am so tired.  Any suggestions would be greatly appreciated. I feel as though I am the only parent trying to have them grow up to be productive and happy people but the mean and strict one.  And don't want anyone else to continue this cycle.

Please be honest I know that I am not perfect and could do things differently just not sure how.