Legal Question in Family Law in California

Yes, unless you correct whatever resulted in the default being declined and refile it before they respond.

I agree. The clerk has no authority to reject a paper simply because it is late. It is the clerk's entry of default that prevents late filing. You will have to correct and resubmit your paperwork, unless a response has been filed.

Yes, respondent can still respond. If you do successfully obtain a default, then respondent will need to obtain court permission, by filing a motion to vacate the default, in order to respond.