I would recommend you to try to create a new ebook from scratch in Sigil. Just a small one with three or four pages. That way you can ensure that there is no fixed layout. Then test this book on different devices.
It doesn't even have to be the same pictures as in the real books, just the same sizes.
Then, if there still are problems, you can easily upload the book here (or perhaps better in the epub subforum) and ask for help on how to make the book usable on more devices.
After this you can more easily decide how to handle it. Either change the original book to make it usable on any device, or create a special version of the book for the Android segment. Or something else.
You can read more about fixed format epubs here:
https://wiki.mobileread.com/wiki/Fixed_layout_ePub
Since Android devices comes in many different sizes, fixed layout is usually not a good idea for that platform...