Wanting both Xbox systems to show up in accounts & email.

Both your Xbox 360 and Xbox One are already showing up on your account. I'm sure what you're asking for. https://account.xbox.com/Profile?gamerTag=BABY+BOOP+913

I tried both. When my husband's account is used, it shows my husband's xbox gamer tag. When I used my account to sign in, it wants me to create an account.

When we set up his xbox account we used an outlook email address for my son.

There is no way to merge email accounts, the best solution would be to have both account on your system so you can continue using the gamertag you want, with the console Home set to the account that you purchase your games on.

This way you will have both on your system without any issues.

Yes basically you want to separate yourself from that account. So take whatever email you want to add as your new main email. Add that to the current account as an alternate email address. Then make that email the new main email for that account. You want to do the same thing with your parents account as well. Make sure you've added both emails as alternate emails to BOTH accounts. Which would free up your parents email and separate the accounts. You could then remove their email entirely from the account (once your new email has been added).

Then you will be all set.

Yes basically you want to separate yourself from that account. So take whatever email you want to add as your new main email. Add that to the current account as an alternate email address. Then make that email the new main email for that account. You want to do the same thing with your parents account as well. Make sure you've added both emails as alternate emails to BOTH accounts. Which would free up your parents email and separate the accounts. You could then remove their email entirely from the account (once your new email has been added).

Then you will be all set.