I read a lot of manga, which uses something like that "the main character died, but woke up in his(her) past in his(her) young body.
But whatever I read, the hero is always alone. Is there a manga (mangha) where 2 or more characters die and go back in time?

Just A Girl He Knows fits quite well
Live or Not doesn't involve time travel, but the characters do revert back to their younger selves

Does reincarnating 500 years into the future work? Seijo ni naru no de Nidoume no Jinsei wa Katte ni sasete moraimasu Outaishi wa, Zensei de Watashi wo Futta Koibito deshita

~4400 manga completed
~1700 ongoing...