Anon,
How can I make the right decision on possible choices between using a possessive or using an adjectival form? You are asking a very general question which requires a lot of answers. Basically, I will tell you, read more, listen more and use English more so that you can develop a second-nature to English.
... is a magazine featuring regular columns such as chapter group news (why not 'chapter groups' news'??)
I am scratching my head and I have no clue what a “chapter group is…!
important to raise learner awareness (why not, 'leaners' awareness??) I supposed you meant more than one learns, right? In that case, “learners’ awareness” is ok. We can not use rigid formulas on English because contexts dictate what words and tenses to use.
Also, which one is correct, 'of' or 'out of'? ---“Of”
Of the three people (who) I had to call to ask for their possible involvement in our event as volunteers, two had responded positively saying they would.