You're using responsive to two different ways... It's a little confusing. You want the iframe to size itself correctly (responsively) and you want the scrolling to work properly (to respond to user input)... I think?
There are a whole lot of reasons why you should give up, and may I suggest that you do?
Take a look at adapt-launchNewWindow. This is really the only solution to your problem - forcing the content to load in a new window on ios.
But... If you really want to get your head around why you should do that...
Even after those suggested fixes, you're still going to have position: fixed issues (which means trickle, navigation bar and notify problems) css rendering issues, general laggyness and lots of rerendering, layout thrashing, tearing, etc etc, ios was never really designed to support iframes with scrolling content...
If you've got nested iframes... god help you... :/