How to add an InfoWindow object and 2 markers to bounds?

Question

Google Maps

Hello! It is necessary for me that 2 markers + InfoWindow open on one of them are displayed on the map. Now I'm trying to use the following code to search for bounds:

function calculateWaypointsBounds(attraction, destination, client, infoBox, map){

  const bounds = new google.maps.LatLngBounds();
  bounds.extend(new google.maps.LatLng(attraction.lat, attraction.lon));
  bounds.extend(new google.maps.LatLng(client.lat, client.lon));
  bounds.extend(new google.maps.LatLng(destination.lat, destination.lon));

  const div = infoBox.content_;

  const projectionCoords = infoBox.getProjection().fromLatLngToContainerPixel(new google.maps.LatLng(attraction.lat, attraction.lon));
  const leftTop = new google.maps.Point(projectionCoords.x - div.offsetWidth / 2, projectionCoords.y - 400);
  const rightTop = new google.maps.Point(projectionCoords.x + div.offsetWidth / 2, projectionCoords.y - 400);
  const ltCoords = infoBox.getProjection().fromContainerPixelToLatLng(leftTop);
  const rtCoords = infoBox.getProjection().fromContainerPixelToLatLng(rightTop);

  bounds.extend(ltCoords);
  bounds.extend(rtCoords); //InfoWindow always shows above marker, so i'm need only top left and top right corners.

  return bounds;
}

But something to determine the coordinates of the right and left corner of the InfoWindow does not work.