MMC and FMC have older siblings. These older siblings get married then die. MMC and FMC get truck-kunned into the past where they try to keep their older siblings from meeting each other, re-falling in love or finally expressing themselves to each other.

Thank you for your help.

is it Goodbye In-Law
the mcs hate each other bc of something that happened in highschool and then they find out their sibling get married. a fortune teller tells them it’s destined to be fatal or misfortunate, but they get married anyway. and on the day of their wedding, they get into a car accident.

hope this was the one you were looking for

The title is
Goodbye In-law

https://www.mangaupdates.com/series.html?id=156109

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