I did a little more research and honestly I think most of this is an Apple issue. If you do a search on Google/Bing you will find lots of Apple users who were complaining about not being able to check a checkbox on various websites. It seems to be something to do with the css styles used and how Apple handles them or something like that. These were somewhat recent too, I could find people just last year saying it was still happening.
As far as grid edit goes you could try submitting it via
User Voice and see if enough other people feel the same way as you. If things there get enough votes they can possibly be implemented. I wish I had a better answer for you but iPads just don't seem to be great to use with QuickBase.