
Its been a while since i read this.. so i get that there are 4 sons: Eunghyuk, Eungyo (ml), Eunho, and Eunsoo.
Why are they all ganging up against Eunho..
and if Eunhyuk is the oldest, why does it seem like he is subordinate/yields to Eungyo??

The reason they were all ganging up against the third oldest siblings(Eunho) was simple. Their father promised that whoever among the siblings gave him a grandchild will surely get an inheritance.
Eunhyuk is not a subordinate to Eungyo, they works in the same company but his big brother work in different department. Even in the novel, the one who listens to Eungyo problems and gave him advice was always the oldest, so in a sense Eungyo always respect Eunhyuk as a big brother.
Family chart: Eunhyuk(oldest), Eungyo(2nd oldest), Eunho(third oldest), Eunsoo(youngest siblings).
Urghurghuhuu the lovey dovey of this tsundere is unmatched...