- (void)viewDidLoad {
    [super viewDidLoad];
    NSMutableArray *markersArray = [[NSMutableArray alloc] init];
    for(int i=0; i<10; i++){
        GMSMarker *marker = [[GMSMarker alloc] init];
        marker.position = CLLocationCoordinate2DMake(latitude, longitude);
        marker.appearAnimation=YES;
        marker.opacity = 0.0;
        mapView.selectedMarker = marker;
        marker.map = mapView;
        [markersArray addObject:marker];
    }
}

- (UIView*)mapView:(GMSMapView *)mapView markerInfoWindow:(GMSMarker *)marker {
    CustomInforwindow *customView =  [[[NSBundle mainBundle] loadNibNamed:@"CustomInforwindow" owner:self options:nil] objectAtIndex:0];
    return customView;
}

mapView.selectedMarker = marker; this will open the infowindow for the last marker

marker1.position = Locationcoorsinate2dobject;
marker2.position = Locationcoorsinate2dobject;
marker1.tappable = false;
marker2.tappable = false;

marker2.icon = [UIImage imageNamed:@"yourinfowindow.png"];
marker2.groundanchor = CGPointMake(marker1.groundanchor.x, marker1.gorundanchor.y + 2‌​.7);