Regarding uber trist and ancients: they are not an issue, I've done both several times now with a blood boil build.
Demons used: Cursed P8 urdar or lancer. (Others may work too, haven't tried it.
Kill bosses one by one.
Uber Trist: Port your demon + 1-2 goatmen on the boss you are killing, use sigil lethargy. Resummon goatmen as needed. Use blood boil freely when there are adds you can engorge. Use hardly at all when not, you don't want your demon to get killed.
Uber ancients: Same procedure, just without engorge. You can use blood boil as long as your demon doesn't drop too low, resummon goatmen when they die. If you are squishy, you may want to keep the distance and port your summons to the boss you are taking on.
Gear used: Obsession, Enigma, Magefist, Soj, Soj, Arach, Baalos, Wraithstep, 3demon 20fcr circ, 3demon 100 life amu, Anni, torch, 9 demon skillers