Is the rendering of 相 into English as "mutual(ly)" sensible?
少欲俱相類，相聚，相應，相可 《雜阿含經》

少欲者俱相類，相聚，相應，相可 《佛說相應相可經》

少欲者: 貪欲少的人、欲望較少的人 People with less desire

俱: all

相類: 互相類似 They think and behave similarly.

相聚: 互相聚集 They often get together.

相應: 互相契合 They tally or correspond mutually.
相應 means to tally or to correspond (契合) in Buddhism, not to react or to interact.

相可: 互相許可 They agree with one another. They agree mutually.

相 may mean "mutually" or "each other".
However, one is an adverb, and the other is a pronoun.
I think the 相 in 相類, 相聚, 相應 and 相可 are more likely to be the adverbs, not the pronouns.
So, 相 means "mutually" here.