Stepparent Supportive Declaration

My question involves a child custody case from the State of: California
My husband's ex is seeking sole physical custody of two teens. They have had equal custody for 9 years. Ex names me in her declaration and says I abuse her kids which is ridiculous.
Question: Is it appropriate or useful for me to file a dec of my own in support of his opposition to the OSC?

Submit it to whom for what purpose?

If the matter goes to hearing, I expect your spouse and his lawyer will want your testimony.