In some states, a GAL, Law Guardian, or similar is now appointed as a matter of course in all custody cases. Most leave it to the judge's discretion, and some judges appoint GALs for nearly all cases, while others only do so in specific circumstances. You did not provide the name of your state, so I cannot present any laws regarding the matter.
In any case, the GAL is not "appointed to your in-laws"; a GAL's purpose is to investigate and testify to the court in an unbiased manner regarding the child's best interests.