is dojin's parent both male? and does his sister also need to marry female or is it male?

Nope. They have alpha dad and beta mom. The alpha sister (if she wants) can only impregnate male/female omegas and female betas

Yes. I forgot which chapters but it mentions "besides dojin "mom" everyone are alpha".
So it's possible if his mom is a male omega. Like every omegaverse fics, the one who give birth will be called mom and sometimes dad.
She isn't obligated to marry or to find a mate, though fargo once shared a drawing of her fricking a male with her peepee, cowgirl style

dojin's "dad" is an alpha male and his "mom" is an omega male.

Noo if the mom was a beta, heesoo and dojun would be able to have a baby (i hope the author changes it ) and in one of the chapters it said "everyones an alpha except for mom".

Both of Dojin’s parents are male. I don’t know anything about the sister though (￣∇￣")

Uhhh link

https://13-fargo.postype.com/post/6198409 (also need to login for age confirmation)

Thank you

someone told me their mom is also a he