Come inserire 2 immagini in un unico luogo Flutter

Se il problema è sulla sovrapposizione di due widget, è possibile utilizzare Stack a gestire la cosa.

È possibile utilizzare un Stack con Positioned per fare questo: Ecco un Esempio con le icone:

class StackExample extends StatelessWidget {
  @override
  Widget build(BuildContext context) {
    return new Scaffold(
      appBar: new AppBar(),
      body:  new Container(
        padding: const EdgeInsets.all(8.0),
          height: 500.0,
          width: 500.0,
          // alignment: FractionalOffset.center,
          child: new Stack(
            //alignment:new Alignment(x, y)
            children: <Widget>[
              new Icon(Icons.notifications, size: 36.0, color: const Color.fromRGBO(218, 165, 32, 1.0)),
              new Positioned(
                left: 20.0,
                child: new Icon(Icons.notifications, size: 36.0, color: const Color.fromRGBO(218, 165, 32, 1.0)),
              ),
              new Positioned(
                left:40.0,
                child: new Icon(Icons.notifications, size: 36.0, color: const Color.fromRGBO(218, 165, 32, 1.0)),
              )

            ],
          ),
        ),
      )
    ;
  }
}


class StackExample extends StatelessWidget {
  @override
  Widget build(BuildContext context) {
    return new Scaffold(
      appBar: new AppBar(),
      body:  new Container(
        padding: const EdgeInsets.all(8.0),
          height: 500.0,
          width: 500.0,
          // alignment: FractionalOffset.center,
          child: new Stack(
            //alignment:new Alignment(x, y)
            children: <Widget>[
              new Container(
                decoration: new BoxDecoration(
                  borderRadius: BorderRadius.circular(25.0),
                  boxShadow: [
                    new BoxShadow(
                      blurRadius: 5.0,
                      offset: const Offset(3.0, 0.0),
                      color: Colors.grey,
                    )
                  ]
                ),
                child: new Icon(Icons.notifications, size: 36.0, color: const Color.fromRGBO(218, 165, 32, 1.0))),
              new Positioned(
                left: 20.0,
                child: new Container(
                  decoration: new BoxDecoration(
                  borderRadius: BorderRadius.circular(25.0),
                  boxShadow: [
                    new BoxShadow(
                      blurRadius: 5.0,
                      offset: const Offset(3.0, 0.0),
                      color: Colors.grey,
                    )
                  ]
                ),
                  child: new Icon(Icons.notifications, size: 36.0, color: const Color.fromRGBO(218, 165, 32, 1.0))),
              ),
              new Positioned(
                left:40.0,
                child: new Container(
                  decoration: new BoxDecoration(
                  borderRadius: BorderRadius.circular(25.0),
                  boxShadow: [
                    new BoxShadow(
                      blurRadius: 5.0,
                      offset: const Offset(3.0, 0.0),
                      color: Colors.grey,
                    )
                  ]
                )
                  ,child: new Icon(Icons.notifications, size: 36.0, color: const Color.fromRGBO(218, 165, 32, 1.0))),
              )

            ],
          ),
        ),
      )
    ;
  }
}