ml's father is grandma's own flesh, so ml is related to grandma by blood
fl's father is grandma's stepson so there is no blood relation to grandma
ml and fl come from different families, different set of parents

grandma divorced her first husband for having another lover, then remarried, but did not get along with her stepson, and has been estranged from him for decades, so she lives in retirement home since she has no other family and her grandson lives abroad

fl is the only person who visit grandma regularly and has a very close bond with grandma.
ml wrote to grandma regularly over the years, but grandma has never mentioned her stepson nor his family to ml and never mentioned her past or grandson to fl, so neither the ml nor the fl ever knew each other existed. All the ml know is that grandma married into another family but he knows nothing about that family and grandma never talked about them.

But upon ml's return home and visit grandma, grandma mentioned fl to him because she knows fl works in the same company Yueda Group as her grandson who is high level, and knowing her grandson well, before he even said anything, told him to not bully her.

Where did you get she didn’t get along with chenhuan’s father ? 

 Luckyforever:

Is she paternal or maternal grandmother to ml?

maternal. Otherwise Grandma would have asked Yao Ziming How's xyz? rather than How's your Dad? (I remember it is from one episode where YZ visits his Grandma)

 Ashu Singh:

his mother is dead i think

Yea.. right! 

 Ashu Singh:

ml's mother is grandma's own flesh

Episode 19 and we finally get clarification that ML's father is Grandma's son.