Ummm... is she ok?
I would translate like: My grandmother is sitting on the street (not on the road)
हैं why? It's respect for grandma? Because it's not plural...
Yes. Honorific plural.
Why not मेरी दादी सड़क पर बैठ रही हैं।?
My question too!
Is it because:
"The Hindi words for "sitting" and "standing" describe a state of being rather than an action"?
Yes, that is what was explained for other similar sentences on Duo.