1994 Volvo 850 Door Locks Stuck

I purchased this car about 6 months ago. At the time we discovered that the rear driver's door wouldn't open. We dismissed it as minor as we don't often have passengers. Now, however, neither of the rear doors will open. The doors don't unlock w/ the front doors nor can you pull up on the lock from the inside to open it manually. Now, the front passenger door won't open from the inside.

We considered using a "Slim Jim" to open the doors to access the locking mechanism. But if you can't pull up the locks from the inside, will a "Slim Jim" work? Is this a problem with the child locks or the power locks?