I've identified all those I know and those I didn't from the tags.
I don't know who the remaining 3 characters are, the blue armoured swordsman next to Urameshi and the purple haired guy behind Taikoubou seem really familiar but I can't figure them out.
Although I'm not sure who of the remaining characters is from rakudai_ninja_rantarou. I tried to google search it but I can't seem to find out.
Corrected Hamel's name. "Hameln" refers to the island where the mazoku make their home; his name was spelled in that manner in a fansub that made a translation error.