Chuck, there's no reason for you not to place strings of dialogue together like that, but hear this: whatever you do in your story should have a precise reason behind it. Placing three or four sentences, or nine or ten, just because you want it to go a particular length is rather arbitrary. If you're going to do this, you'll want to read other writers who do this to give yourself a taste of how it's done well. James Clavell does it in Shogun, so does Philip Roth, and Roberto Bolano, I believe. And understand that a paragraph stops because the idea it's covering is through being covered, not because you think it's long or short enough. There's nothing wrong with having short two or three word paragraphs, dialogue or no.
Stanmiller already hit the nail on the head about tags. If you write it real enough, it will be obvious to the reader how said character is speaking and who is speaking it. Remember that each character should speak like themselves, not you or each other. Character A might say, "We should try to get out of here", while B would say, "We're going. Now!" It's a matter of who the speaker really is. If you capture these cadences, it will give the reader subtle hints into the character while helping them know who is saying what without unnecessary denotations on the page.