#1
D on bottom
F# in the middle
G or Abb on top.

i was thinking that it was just a D major chord with a double diminished 5th, but as an isolated chord, you cant have flats in the key of D.

maybe it really is just Dddim5, but i have no clue.

keep in mind i have a AP music theory education from high school, so this is my best guess.
#2
D Major with an added 4 (Dadd4)

without the fourth. Or it could be an inverted G Major 7 chord.
WHY IS EVERYONE IN THE PIT A FUCKING METALCORE KID
#4
Hmm.. it could be a Dadd11 without the 5th, or it could be a Gmaj7 without the 3rd. It would depend on the progression. Both are equally likely AFAIK.