How to pull latitude and longitude coordinates from firebase realtime database within a certain radius android studio

Question

I have set up a firebase realtime database with locations set up with both a latitude and a longitude in each node. In my android app, I have set it up so that it saves the user's initial location and then compares it to the latitude and longitude in the realtime database. I want to pull only the locations that are within a certain radius. I can't seem to find a way to create a function that would be able to do this. I can't use firestore because other aspects of my system rely on the realtime database.

This is the code to get the user's inital location on creation

 Location initialValue = new Location("firstvalue");
        double[] firstcoordinates = getGPS();
        initialValue.setLatitude(firstcoordinates[0]);
        initialValue.setLongitude(firstcoordinates[1]);

This is the getGPS function used to get the location

 private double[] getGPS() {
        LocationManager lm = (LocationManager) getSystemService(Context.LOCATION_SERVICE);
        List<String> providers = lm.getProviders(true);

        /* Loop over the array backwards, and if you get an accurate location, then break                 out the loop*/
        Location l = null;

        for (int i=providers.size()-1; i>=0; i--) {
            l = lm.getLastKnownLocation(providers.get(i));
            if (l != null) break;
        }

        double[] gps = new double[2];
        if (l != null) {
            gps[0] = l.getLatitude();
            gps[1] = l.getLongitude();
        }
        return gps;
    }

The inital location return works great. The issue is pulling only the values within a certain radius. Currently, the code below pulls all the locations.

public class MapsActivity extends FragmentActivity implements OnMapReadyCallback {

    public static FirebaseDatabase mDatabase = FirebaseDatabase.getInstance();
    public static DatabaseReference mReferenceCrossings = mDatabase.getReference();
    public static ArrayList<Location> results = new ArrayList<Location>();
    String reference = "Crossings";
    String orderKey = "Latitudes";



    public ArrayList<Location> sortedQuery() throws InterruptedException {

        return results;


    }


    interface FirebaseCallback {

        void onCallback(ArrayList<Location> locations);
    }

    private ArrayList<Location> readData(FirebaseCallback firebaseCallback) {
      ValueEventListener() {
            @Override
            public void onDataChange(@NonNull DataSnapshot datasnapshot) {
                for (DataSnapshot child : datasnapshot.getChildren()) {
                    double latitude = Double.parseDouble(child.child("Latitude").getValue().toString());
                    double longitude = Double.parseDouble(child.child("Longitude").getValue().toString());
                    Location entry = new Location("coordinates");
                    entry.setLatitude(latitude);
                    entry.setLongitude(longitude);
                    results.add(entry);
                }

                firebaseCallback.onCallback(results);
            }

            @Override
            public void onCancelled(@NonNull DatabaseError error) {
                Log.d("Firebase error", error.getDetails());
            }

        });
        return results;
    }

This is the firebase realtimedatabse with the values being used.

I only want to pull values within a certain radius, say 30 kms, instead of all of them. I would appreciate any help. Thank you so much.