We are looking for calendars subscriptions for Islamic and Jewish holidays which show up in English - for our Apple calendars. We have found them in native languages which we are not fluent in. Where can I find these? 
in advance.
When you say “Apple calendars,” do you mean iCloud calendars, or just calendars that you use in the Calendar app?
If you mean iCloud calendars, I don’t know.
But it’s easy to add Google Calendars to the Calendar app, and Islamic and Jewish calendars are readily available in Google. On the main Google Calendar page, click the + next to “Other calendars” in the sidebar, then “Browse calendars of interest.” “Global Religious Holidays” will be one of the first options you see, and Islamic and Jewish holidays are both there.
For Jewish holidays, this works well. Lots of choices. Jewish Holiday downloads for desktop, mobile and web calendars - Hebcal