The heavily biased (in favor of the Trinity) NIV Study Bible note on Genesis 1:26 -
“God speaks as the Creator-King, announcing his crowning work to the members of his heavenly court (see 3:22; 11:7; Isa 6:8; see also 1 Ki 22:19-23; Job 15:8; Jer 23:18.)”
Not three deity persons talking to himself (or is it themselves?) but the Father (see the Apostles’ Creed) announcing his crowning work to the members of his (not their) heavenly court.
The note goes on to address likeness and image:
”No distinction should be made between ‘image‘ and ‘likeness,’ which are synonyms in both the OT (5:1; 9:6) and the NT (1 Co 11:7; Col 3:10; Jas 3:9). … ‘Image’ includes such characteristics as ‘righteousness and holiness’ (Eph 4:24) and ‘knowledge’ (Col 3:10). …”
(The NIV Study Bible, 10th Anniversary Edition, p.8)
Man was created by Yahweh and so were the angels. Are the characteristics in the NIV applicable to angels? Who will accuse them of being unrighteous and unholy? Who will say that they aren’t knowledgable about their creator?
There are differences between men and angels but there are also similarities.
God (Heb. elohim, plural in form, singular in meaning; Gk. theos, singular in meaning) speaking to the angels (Heb. elohim, plural in form, plural in meaning) before the creation of man by God is entirely reasonable.
Deity persons talking among himself (themselves?) is a concept unknown to Moses.