I bought one of the Kindle Fire 7'' six-packs; my Kindles are a mix of Fire OS 5.0.1 and 5.1.1. But, the app I'm using to collect data for my research doesn't work with Android or Fire OS 5. I need to install Android 2, 3, or 4. I found a way to root my devices (RootJunky's SuperTool). I'm confused about what to do next. It looks like I need a custom ROM and a custom bootloader? TWRP only works with 5.0.1 right now...is there an alternative that I can use with the 5.1.1 devices? All the articles I find online are from 2+ years ago, so I'm not sure if the instructions will work with these devices / OS. Thanks for your help providing more current information about what to use!