Complex sentence: Mrs Devine's duty was to prepare the courthouse for mass. She was allowed to do so, but was accompanied by one of the Kellys, at about 10 am Kelly remained in the courthouse and helped Mrs Devine prepare the altar and dust the forms.
Split into simpler sentences: Mrs Devine's duty was to prepare the courthouse for mass. She was allowed to do so, but was accompanied by one of the Kellys. At about 10 am Kelly remained in the courthouse and helped Mrs Devine prepare the altar and dust the forms.