Each Other's or Each Others' / One Another's or One Anothers'

English as a Second Language English Vocabulary, Grammar and Idioms
1

Upon each others’ hearts … OK?

With all of the people in this group, we can hurt one anothers’ feelings very quickly.
(More than 2 in the group)

They hurt each others’ feelings (OR other’s feelings)?

Where does the apostrophe go?

They hurt one anothers’ feelings. OK? (More than 2 people)

Others’ feelings were hurt. OK?

Please tell me the answers to each because I’m confused with this one.

2

Upon each other’s heart
With all of the people in this group, we can hurt one another’s feelings very quickly.
They hurt each other’s feelings
They hurt one another’s feelings. (More than 2 people)
Others’ feelings were hurt.

Each, one, and another are all singular words only.