Backups are the best friends of anyone who gets close to a computer.
By now you should have a copy of the content that might interest you from the SSD with W7, and even from the W10 one.
To see the SSDs in tools like HBCD you should use a more current version.
My experience with multi-booting on desktops always ends with the recommendation to put a disk rack with independent power, like this one, because of the advantages it offers.
Be clear about what you want to achieve, and forget about using W7 recovery tools, if you don't want to mess up access to W10.
If the one with W10 interests you less or you're willing to reinstall it (I get the feeling that here you imply that you reinstalled it again and that could be the origin of the problem), if you have two identical SSDs, you leave only the one with W10 whose relevant content you already have saved elsewhere, you install W7 from scratch and when you're already in the file copying phase after booting from the SSD, you exit (if you want to do the full installation it's up to you, it's to save time), you turn it off, you connect the second SSD and with a program like Ghost or any other that allows you to clone partitions, you overwrite the partitions of the SSD you want to recover on the one you just installed.
You remove the damaged one again, and you try to boot, and it should work.
All this is thinking that you haven't been touching anything in BIOS, nor have the SATA data cables fallen to pieces or similar things.
Best regards.