I've seen it done several ways. Chapter title, then POV tag, then text is one way to communicate it unambigously.

If they're distinctly different voices, it's not necessary. Trust your readers.

The most important thing to know for now, though, is that you're writing a first draft. You can always tweak the details later - assuming YOU know which chapter belongs to which voice. So just write, and worry about chapter headings later. That's my advice, for what it's worth.