Yup, thats why we stopped at Bonethrasher, we knew it is impossible to 4 man Fabricator.
Impossible? Probably not. I'm sure there would be a way to do it with 4. Something like have the healer and the Jugg on bottom and Mara and PT on top. Have them solve the puzzle. PT jumps down and taunts, Jugg jumps up to Mara, Mara jumps down and does dps while burnt. Mara runs back up and helps Jugg finish puzzle.... After that I'm kinda lost.
Infernal Council requires 8 people
Not sure that is true... If I understand how the mechanic works (which I'm not claiming I do) it could be solo'd. From what I understand you get the debuff if you are not the first person to attack the council member. Meaning after the first four are killed, the second four could be killed. Would need to test this though...