Can not log into profile as yahoo email does not exist and cant verify account with microsoft

You may please phone the support on your issue as they are able to help with this. The proper phone number can be found at
support.xbox.com/contact-us

Anyway you may encounter a 30 day suspension of your account for security reasons if they change security information for you. By this they prevent your account from being stolen.

For Microsoft related emails like Hotmail, outlook, once they are in any way attempt to be logged in with the XBOX console or server or be attach to another xbox account, it will have the system directly note that it has an existing gamertag linked to it.
You may need to create a new one or the one from a third party like gmail or yahoo. You can also contact chat support to verify if you can pull up an account by searching using the outlook email you have

[quote user="AdriiiXx"]I'm sure that the email and the password are correct because if I try to log in in the email using the same password it accepts me, but not when I try to accept the terms of use.. (my parents' mail is a @yahoo one, is that a problem?)[/quote]

Your parent's email being a Yahoo! Email is not really a problem.

But from the sound of it, the email wasn't made a Live ID account yet.

Let me explain:

The Xbox Live service authenticates users by the "Microsoft Account" (or formerly Live ID).

The username for this Microsoft Account "looks like" an email address.

If you use Microsoft services like Hotmail/Outlook, Live.com and the likes, the username that looks like an email, is in fact an email on the Live service.

If you use a third party email like Yahoo, Gmail, other freemail services or your own domain, then these email adresses are
NOT YET a Microsoft Account.

In order to resolve that, your parents have to go to
https://signup.live.com and make their Yahoo Email a Microsoft account.

REMEMBER! When your parents create a Microsoft Account with their Yahoo Address, that this Microsoft Account is a
SEPARATE account from the Yahoo Service. While the Microsoft Account Username
LOOKS LIKE the Yahoo Email, it is just a string of characters, that resembles the Yahoo Address, but has no connection to the Yahoo email otherwise.

This means that the Password can (and should be) different from the Yahoo Email.

Additionally, if the Yahoo Email should get deleted, the Microsoft Account with the Yahoo email will
continue to exist!

--

So to sum it up: Your parents need to
create a Microsoft Account with the Yahoo Email first.

My current email has been the only alias on my account for the last 6 months and Microsoft does not recognize the yahoo as a user when I attempt to log in with it. I honestly forgot its existence until now and it mystifies me that its still attached in
any way.

If you're signing in with your Yahoo! email, then isn't your goal already accomplished? Or are you trying to assign your gamertag to another Yahoo! email? Trying to sort out exactly what it is you want to have happen. Are you stating that you don't want
your Gamerag to have a "Microsoft Account"? All Xbox profiles branch from an attached "Microsoft Account". Even if you log in with Yahoo!, or Gmail, or an AOL email, it will always be referred to as your "Microsoft Account", because it is the email and password
with which you access any Microsoft services attached to that Xbox profile.