Section 12 and section 25 of gurdian and ward act.

What is your query? You may consult the bare act to understand the law. 

When a case under section 12 is pending in high court can someone file another in family court under section 25 for custody?

Yes that is possible. Section 12 of the GW Act is with regard to Interlocutory order for production of minor and interim protection order of person and property of the minor whereas, under section 25 the lawful guardian is resorted with the custody of the minor child who is removed from his/her the lawful custody. Where in former case a temporary custody is being made by the court in favour of someone else from the custody of the person holding such custody, not necessarily, the lawful guardian while in the later the court is restoring the lawful custody of the minor to the lawful guardian. The former case is temporary arrangement while former is permanent arrangement with regard to custody of minor of its person and property.