Typically ら is used to form plurals or groups of people in casual situations, when it is used pejoratively, or in set words such as 彼ら. たち seems to be prefered in other situations ○○さんたち、あなたたち、 私達, etc.
However, I have noticed that ら is also used a lot in news, such as 新宿警察署 新たに警察官ら５人の感染確認and in the science magazine Newton, such as 名古屋大学の田中実教授らは….
Here, ら is neither casual nor pejorative, and is used towards those worthy of respect. How did ら develop such a divergent usage? How would the nuance change if we used たち instead of ら here?