Can a family court order joint decision-making even while a child protection file remains open?

Yes, it's possible - an open child protection file doesn't automatically prevent a family court from ordering joint decision-making responsibility between the parents, since the two proceedings are legally separate and the family court makes its own assessment of whether joint decision-making serves the child's best interests given the current situation. If the concerns behind the protection file relate to one parent's home specifically, and the other parent's ability to share decision-making isn't in question, a court may still see joint decision-making as workable, sometimes with practical adjustments.

That said, a court is unlikely to order joint decision-making where the open file raises real doubts about whether the parents can communicate and cooperate effectively, since joint decision-making generally requires a working relationship between the parents to function well in practice - an active protection concern involving conflict or an inability to cooperate can work against it for that reason, separate from the merits of the underlying concern itself. If joint decision-making is what you're hoping for while a file remains open, be prepared to show the court that the concern doesn't affect your ability to cooperate with the other parent on the child's major decisions.