second/third conditional

At 51 seconds, this is what Cooper says:

You know, one of those "useless machines" they used to make was called an MRI.

And if we had any of those left, the doctors would have been able to find the cyst in my wife's brain before she died, instead of afterwards. Then she would have been the one sitting here listening to this instead of me, which would have been a good thing 'cause she was always the calmer one.

I have several questions regarding the quoted conversation above:
(1) Why did he say "if we had any of those left" instead of "if we had had any of those left"?

(2) Can the second "would have been" be replaced with "would be", as in "Then should would be the one sitting here..."

(3) Can the third "would have been" be replaced with "would be", as in "...which would be a good thing"?