The third son is a child of 2nd wife.
The family is swordmaster/warrior.
1st Wife's Family is an assassin disguised as a merchant family.
The third son had hidden potential and wanted to be lazy.
The 1st wife wanted to kill the 2nd wife but in turn, retaliated by the third son.

That is all information I can remember.

Thanks in advance.

Pretty sure that is "The Lazy Swordmaster".
(novel) NU link: https://www.novelupdates.com/series/the-lazy-swordmaster/
(novel) MU link: https://www.mangaupdates.com/series.html?id=135389
According to NU there is a manhwa adaptation but I do not see it on MU

I did see similar manhwa/manga to the lazy master just I don't know if I am dreaming or what. Anyway thanks for reminding me @lollylopmr