Nothing much you can do in term of forms, maybe bench them a few matches. But then Cup games are not usefull as benchmarks coz you're always up against stronger teams or even solid abandoned teams.

You are probably unlucky because your team all hit their peak last season, so logically there's a downward cycle. For you it seems to happen for a wider range of players since they all performed last season, as you said. Ride it out and play more friendlies.