The Archangels, Fargo, Phaedra, Zera, Sophia, and Azrael all contribute to making an explosion half the size of a galaxy.
That's the statement, so let's go.
I'll use the Milky Way for the standard size of a galaxy, which has a radius of 52850~ light-years.
52850/2 light-years = 250006925000000000 km
This will be used for the radius of the explosion.
Explosion Yield Formula
Y = ((x/0.28)^3)/1000
Y = ((250006925000000000/0.28)^3)/1000 = 7.1183e^53 Megatons
7.1183e^53*1000 = 7.1183e^56 Kilotons
7.1183e^56*1000 = 7.1183e^59 Tons
1 Foe = 2.39e^34 Tons
7.1183e^59/2.39e^34 = 326,806,360,568,621,027,719.665271966527196 Foe
= 326.80636 Exafoe
5 people contributed to this explosion.
326.80636/5 = 65.361 Exafoe
Blast Yield: 326.80636 Exafoe (Multi-Solar System level) Scales to the Durability of Archangel's Forcefields.
Individual Yield: 65.361 Exafoe (Multi-Solar System level) Scales to the Attack Potency/Durability of the Archangels.
Pretty good results.