Greetings again Matthias,
My recommendation to you - as it would be to all - is to consult as many Bible dictionaries as possible for information on the angels. And just as with all sources: read widely, deeply, thoughtfully and critically.
Yes, but in practical terms as relevant to the situation in our Ecclesia, I doubt that I would suggest the ivp three volume Illustrated Bible Dictionary that I know is in the reference library, or any other of the dictionaries that may be there.
If an older brother was going to do a series on The Angels, or a younger brother was to give a lecture on Angels then I would suggest the following resources:
Angels, God's Messengers - Bible Teaching about God's "Ministering Spirits", Stanley Owen, 16 page, Christadelphiam Magazine and Publishing Association Birmingham UK
The Truth about Lucifer - the "Devil" not a Fallen Angel, John Ullman, 16 page, Logos Publications Adelaide South Australia
Angels - God Servants, Ian Budden , 16 page, Printland Publishers Hyderabad India
The Angels that Sinned - "Slandering celestial beings", Stephen Cox, 28 page, Printland Publishers Hyderabad India
Demon Possession John Allfree, 16 page, Bible Study Publications, Mansfield, Nottinghamshire UK
The Devil, the Great Deceiver, Peter Watkins, 128 page, Christadelphiam Magazine and Publishing Association Birmingham UK
The Devil Exposed, Mr Epps, 147 page, Printland Publishers Hyderabad India
There are at least two series of studies in mp3 format and slides. One by Ron Cowie, South Australia, and one by Jim Styles, California, USA.
There may be some articles in the four major magazines.
Kind regards
Trevor