Can two parents share one email address?

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 rarely uses email

Every family member needs an email address. Add them as a family member (a grandparent, a babysitter) using any address they can read. They never have to sign in: they pick up with their own 4-digit pickup code, which the parent who added them can share with them from the app, or which you can reveal from their row.

Related: Invite parents to the app, Reveal or reset a pickup code, Share a pickup code with family.