Rek'Sai and Baron Nashor Relation

No and no.

They are both from the void, and maybe they look a bit closer to each other than other void creatures.

But the resemblance is barely high enough that you put them togetehr in anything mor than what makes a "reptiles" or "mamals" type group over there.

Dunno, guess you'd have to know what baron looks like from the neck down?

To me Rek'Sai looks like Baron's Daughter

well in the game blitzcrank poro roundup baron walks on 4 legs reksai have 4 legs too head look same too for me reksai is daughter of nashor