The judge setting a bond is a positive development, but the Alabama detainer is the complicating factor that may prevent release even if the bond is paid.
Here is how detainers work in practice. The Alabama Department of Corrections placed a hold on your brother-in-law specifically to prevent him from being released before they take custody. Even if the Florida bond is posted and satisfied, the jail may not release him into the community because the detainer requires them to hold him for Alabama to pick up.
The sequence that typically plays out is this. Florida resolves its local matter, whether through bond, time served, or case disposition. At that point, instead of walking out the front door, your brother-in-law transfers into Alabama's custody to answer for the parole violation. The bond addresses the Florida side of the equation but it does not dissolve the Alabama hold.
That said, the judge's bond order does carry weight and the situation is not hopeless. If Alabama has not picked him up in nearly 30 days, there may be room for an attorney to argue that the detainer should be resolved differently or that the circumstances warrant release. Some states have time limits on how long they can hold someone on a detainer before they must either pick them up or release the hold.
An attorney who handles interstate detainer situations is the most valuable resource right now. They can communicate with Alabama DOC, assess whether the detainer can be challenged, and give you the most accurate picture of whether bond actually produces a release in this specific situation.