Can two parents share one email address?
No. Each adult gets their own email, login, and pickup code. A family member without email can use a pickup code instead of an account.
No. Each adult in a family needs their own email address, because the email is the login and each person carries their own personal pickup code. Two parents sharing one address would also share one identity at pickup, which defeats the safety model.
Add each adult as their own family member with their own email. Both get the app, both get their own pickup code, and messages show who actually wrote them.
If one adult has no email address
Add them as a limited-access family member. Limited members (a grandparent, a babysitter) do not need an account at all: they pick up with their own 4-digit pickup code, which a full-access parent can share with them from the app.
Related: Invite parents to the app, Reveal or reset a pickup code, Share a pickup code with family.