The status of Yazeed and the position of the narrator Abu Mikhnaf

Q: Could you explain to me the correct opinion regarding Yazeed bin Mu'aawiyah? I read the book "Revealing the True Facts of Yazeed ~ The Incident of KARBALA and the Events that Followed". I found it to be very beneficial, however I have heard that there is a weak narrator by the name of Abu Mikhnaf, who appears in some of the reports quoted in the book. Is this correct? 

The reliability of the book "Revealing the True Facts of Yazeed ~ The Incident of KARBALA and the Events that Followed"

Q: Mufti Saheb, I have heard that some of the narrations in the book "Revealing the True Facts of Yazeed ~ The Incident of KARBALA and the Events that Followed" are quoted through a weak, shia narrator, by the name of Abu Mikhnaf. Is this correct? If it is, then can we quote from such narrators? 

Dua to be recited when leaving a gathering

Q: I have learnt the dua' said at the end of a gathering ("subhanakallahumma wa bihamdika ashhadu...") which compensates for vain talk etc in the gathering. My question is, can this dua also be said in the end of a telephone conversation? Since often much vain talk and possible backbiting etc goes on in telephone conversations. If so, is it OK if I say the dua after having closed the phone at the end of the conversation (rather than saying it whilst still in conversation) in order to not appear weird/strange (since the person I speak with might not understand)?

Birthday parties

Q: My family invited me for a birthday party. Few years before they cut down relation with me because of my in laws but now they invited me for this party respectfully. Is it permissible for me to attend this party for family relationship, otherwise I am not interested in these types of parties.

Marital problems

Q: I have a question regarding divorce. Me and my wife have had a lot of problems. And we end up living separated. But I said once that I give her divorce. But we lived together after that. Then we got problems. I didn't have problems with her. But her family had a lot of problems with me. And I shifted from my wife. I live in Norway. And my wife applied separation in Norwegian law. But I didn't give her divorce. But her parents got some kind of fatwa from somebody in Pakistan that it's a valid divorce. My question is, is it a valid divorce? How is that possible? She wants to comeback as she told me two months ago.

Girls going to school

Q: I go to a public school and I am a girl. Their are male teachers and males at my school but I try to avoid most conversations with other male students. Is it ok to go there? Also I dress modestly nothing revealing. I can't go to an all girls school as its far from where I live.

Imitating the kuffaar

Q: There was a fun run race this past month that is called colour run. Basically the people run a fun run where along the way colour powder gets thrown at the runners. This is a global event which is now becoming prevalent in the Muslim community. The purpose as per their website is celebrating healthiness, happiness and individuality. I would like if Mufti can maybe give a general view on the harms of doing such races and also expanding on the nature of which this is similar to a Hindu custom (Holi)?