Just because cps has opened a case does not mean you are in danger of losing custody. You should speak to your family court lawyer and explore options as to how to best proceed. Good luck.
This answer is only for informational purposes and is not meant as legal advice.
Attempting to stash your children with a girlfriend when cps is looking your direction is not a sound plan. Especially since you indicate you have only been awarded temporary custody.
Far better to engage counsel and address the actual issue(s).
Temporary custody is only obviously temporary while the court decides what is in the best interest of the child. During this period, they will look at what is going on in the child's life and other factors. You would be wise to speak with a child custody attorney to help you in this process.