With regard the video's..... iOS6 has been superceded and in due course, iOS8 will arrive. App makers routinely upgrade their apps to meet whatever the current OS is in order to present an up todate app.
When you or everybody else submit a book to the iBoost store.. the review team will check it meets current store requirements - if it does not - it will get a Ticket and is not accepted until corrections are made and re-delivered.
You have a number of options... deliver the book in its current state and wait an outcome from the review team.
You should consider that iOS6 will be updated on the majority of devices.. so you are limiting the attraction of your book to a dwindling audience over subsequent OS upgrades... and rebuild.
It seems wiser to update the videos to what you can achieve and accept that Apple are always moving forward and by phasing out older options, they maintain quality control of products submitted to their outlets.