Or HaChaim on Genesis 19:13/אור החיים על בראשית י״ט:י״ג

1 כי משחיתים אנחנו את המקום הזה. "For we are about to destroy this place." Although only one of them had been entrusted with that task, the angels used the plural seeing that they were both together. Otherwise the other angel would have appeared as if he was only an assistant.

2Possibly, whenever the Torah speaks of the (avenging) angel Gabriel it is understood that the reference is not only to him personally, but includes his army. Alternatively, since Gabriel was not free to act until the angel Raphael had secured Lot's escape their activities were dependent on one another.