Your brother or brother in law
Great Uncle.
Your borther-in-law's children are your nieces and nephews. You are their uncle or aunt, as is your spouse.
None. There is no relation through "my friend"
Nephews and/or Nieces
There really is no relation, but if the aunt wants to call that half-brother something, call him a nephew. It's only polite.
Uncle if you are male and aunt if you are female.
Your fathers brothers are your uncles. You are their nephew, or niece.
Nephews and nieces
3rd cousin
2nd uncle I believe
You are their great aunt/uncle.
your nephews