You manuscript is ready when you can't find an obvious way to make a major change. But here's the thing, chances are it will never be publishable, regardless of what you, or beta readers, especially beta readers, or hired editor, of anyone else in the world does.
Point to a hundred first time novelists at random, and you can safely bet that not one of them has a publishable manuscript.
This is just how it works. If you put too much time, too much effort, into one novel in an effort to get published, you will probably never be published because you won't get around to writing the novel that is publishable, which, for most, is four or five novels down the line.
Off the top of my head, I can think of about two dozen writers who sold their first novel. I can think of half a dozen who sold the first draft of their first novel. I'm one of them. But this is not the norm.
But here's something else. You said the first two didn't sell because they weren't ready. Chances are that isn't true. A manuscript doesn't have to be anywhere near perfect in any way to land an agent, and a publisher. If the basics are there, if story and character and writing are even close to professional standards, they'll work with you to get it ready. If these things aren't close to professional standards, they probably never will be.
Not everything can be fixed. Bad manuscript nearly always stay bad, no matter who works on them, or for how long.
his said, if you aren't keeping these two novels in circulation, the fault may be with you, not with the manuscripts. Even a very good novel may need to be read by a dozen agents and/or editors before anyone nibbles. Query letter rejections do not count. A rejection on a query letter does not mean your novel was rejected. It only means your query letter was rejected. When you find a way to convince a dozen agents, and a dozen editors, to read your actual novel, and they all say no, then you might be able to say it isn't ready. Until then, you can't know.