Sure. Outsiders may have seen it as different registers of same language. But I doubt if Indians ever regarded Prakrits as a register of "Sanskrit"
Also every Indo-Aryan tongue has a genealogical link to Sanskrit. Hindi does not stand out
Sanskrit is a distinct language. Learn it separately. If you can't speak it, say you don't know it
They are suffused with Latin vocabulary
But that doesn't make them "Latin".
"is"
It is "है" in Hindi. Very distant from the Sanskrit अस्ति
In fact the Marathi आहे (for "is") seems a little closer to अस्ति than है