1.
How you say what you say matters big when delivering a message as serious as an ultimatum. Speak the truth and speak it with as much kindness as you can.
If they aren't able or willing to respect your boundary then at least you know you did it with love and can feel good about the way you asked for care.
Learn how to navigate parenting with a partner who is not on the same page as you when it comes to attachment-focused parenting in this enlightening video that emphasizes the importance of starting with connection, collaboration, and modeling instead of trying to persuade or degrade your partner's way of doing things, and seeking support if your partner is abusive.