Allow duplicate contacts with the same email
You will want to adjust your Deduping and Merging settings (top menu > Contacts > Find and Merge Duplicate Contacts). See https://docs.civicrm.org/user/en/latest/common-workflows/deduping-and-merging/ for info. 

If you're using the default rule that comes when Civi is installed, any contact with the same email will get merged automatically as you're experiencing. It wasn't good for us either because we have so many families and couples who share email addresses.

You will want to 'soften' your Unsupervised rule (the above link has instructions on how to adjust the rules). We changed our Unsupervised rule to take names and birth dates into consideration as well (see image below).  We do get the occasional duplicate contact (Robert Smith with rsmith@example.com is technically not a duplicate of Bob Smith with rsmith@example.com according to our rule), but we'd much rather have easy merges to do than the much more difficult task of 'un-merging' two contacts.