The angels in heaven indeed are sinless. Yet we are not to worship them.
Agreed 100%. But, when the Psalms command the Angels or beseech their assistance, are the Angels being worshiped?
They are not described as omniscient, to my knowledge, so I assume they aren’t.
The Psalmist pleads for their assistance though, doesn't he? And as you've said, Angels are in Heaven, serving God. So, that means either (1) Angels are in fact omniscient, and thus that is another trait not applicable solely to God, or (2) the relationship between Heaven and Earth is one that those is Heaven can "see" all of Earth simultaneously. Thus, if (2) is correct and Mary is in Heaven, is she not able to do the same as the Angels?
Can you help me with a citation for psalm(s) you are referencing?
Not all angels are in heaven all the time as our Heavenly Father uses them as messengers, avengers, in our presence unaware (we are unaware they are angels), protectors, etc. There are many Scriptural passages both in the OT and NT that speak to the different roles angels have played in the history of man and even before man existed.
That angels have sinned (1/3) and rebelled against God and others (2/3) have remained faithful to God is not proof angels are sinless. Only that they have more power than man does to not sin.