Curbing the "Well MY Mom Says..."

[AmyKidsCo]

I would just say what you have written here. It is polite, imho. Anything else just seems to sugarcoat the issue.

I think dad (and mom) need to hear exactly this. And that they are undermining your authority.

I would also do the bye bye outside (drop offs and pick ups) and just eliminate the stress of dealing with the dcps.

Yup. And if it continues you may want to start looking for a replacement. Life is too short to put up with that.