Question about minority interest in EV

Why is noncontrolling interest part of EV continued:

To start, why do we consider the portion of EV called "noncontrolling interest" that at all? Investopedia describes noncontrolling interest as ownership in a company of less than 50%, but according to M&I400, noncontrolling interest in EV is more than 50% stake. Are these two different definitions for "noncontrolling interest?" On a slightly unrelated tangent, is there any meaningful difference in owning 50%+ of a company vs owning 100% of its equity?

Secondly, if EV is to represent a company's "purchase value" does that mean if company A buys company B, company B's 50%+ ownership of company C goes to company A? Can/does company A ever refuse to buy this ownership of company C (asking for theoretical/in practice if possible please)?

Finally, since by GAAP company B puts 100% of a subsidiary company's financials on its financial statements, does it also include 100% of a company C's total equity (whether owned or not by company B) in its EV calculation? 

Thank you in advance.