to a friend's place

[azz]

a. They went out to dinner to friends every Friday.
b. They went out to dinner to friends' places every Friday.
c. They went out to dinner to a friend's place every Friday.

Which could be used if they went to different friends' places on different Fridays? Maybe they had four friends and they had dinner in one friend's place and then the other friend's place and...

Many thanks

[Alan]

All incorrect/unnatural.

--> They went out to friends' places for dinner every Friday.