Use this method to boot remix os.
I had troubles booting it through Grub. THis ISO Entry method shown in the video worked well.
There is one more thing left to try
It can't detect Android x86 because it can't find the source.
Meaning you may have installed Remix OS within a folder named something like this->'/android-2016-xx-yy'
Check if you have.
And if you have, you'll need to edit your Grub entry . You'll need to put the exact folder name after 'SRC='.
So it should look something like this -> 'SRC=/android-2016-xx-yy'