No, you're referring to very broad language families. See my other post or www.ethnologue.com for accurate information.

It's a bit of a tricky business, because what counts as a language is often also determined by political decisions. Mutual comprehensibility is not a reliable criterion. However, modern linguistics uses pretty good sets of "soft" criteria for the classifications.

From personal experience, this is not really true, there are some languages that do maintain some sort of mutual comprehension, but the vast majority in India have no guarantee of that apart from a few choice root words. Speakers of a particular Dravidian language will almost certainly not be able to understand another, and you could make the same argument for Indo-Aryan languages with a very high percentage of success. It's like calling English and French the same language because they have some words that have a similar root. Or even English and German.