Did all Paleolithic ethnicities behave like sentinelenses?

Possibly not. Most hunter-gatherer societies aren't that hostile. Whether they liked it or not, small tribes had to interact with other tribes in order to exchange genes, goods, knowledge to not perish. It's not uncommon for these groups to know several languages besides their own, since they need to communicate with other tribes. The 15-100? Sentinelese alive are deemed to become extinct in that small island if they refuse contact with other human beings.

That's a stupid question. No "all X" ever "do Y." I will point out that all the other tribes in the Andaman Islands who didn't behave like the Sentinelese went extinct.

No, we can tell from indirect evidence.

Sentinelense people act more hostile than stone age people on average because they feel so threatened.

Ethnic groups probably did not exist ast that time.Sentineese are not monolithic