HI there
I have just read your message and you are in a bit of a pickle there to say the least - just want to acknowlede that you sound like a really caring man so more power to you.
Heres a few questions to ask your sister.
What do you want for your children?
How do you see your children's lives progressing?
Do you feel your children are happy and nurtured?
Do you know what your children want to be when the grow up?
Do you feel your children are equipped to go into the world?
Do you feel your children are secure?
How do you rate yourself as a mother and mentor to your children
That's just a few and maybe you could add a few more if you can think of anything. It is important to get your SISTER thinking about her children and see how she responds and even if she gives some smart assed answers or tries to turn it around to put the spot light on YOU - DON'T say anything don't rile her or try to change her mind - just LEAVE those questions with her because trust me - they will stay with her - and let her think about them when you are making efforts to give your nephews feed back on their behaviour.
In relation to your nephew saying YOU ARE NOT MY FATHER AND I DONT' HAVE TO LISTEN TO YOU!!! hate to say it but he is right!!! ALWAYS acknowledge this to him - say to him "John (just using that name as don't know his name) YOU ARE RIGHT (important to say this and not I KNOW IM NOT YOUR FATHER) I am NOT your father but would you consider regarding me as a friend who is interested in your life and gives a damn about teaching you about how you are coming across to people! ALWAYS give him space to make up his mind and don't try to get him to answer you straight away. Say to him - John I am here when you want to talk. ALWAYS acknowledge his feelings and his situation and spell it out to him.!! Spell out his good points and his great characteristics too ie say to him John you are a smart good looking young man you have a sharp mind and a good brain ! (say this even if you don't believe it yourself - but just say it anyway) ask him is this the way he wants to be and if not what does he want and you will be there to help him get it.
I would love to know what you think of this advice and hopefully it will be of some help toyou.
God bless