I believe the description explains this pretty well, but a couple things to point out.
First, when the name 'Bowser' is used in this, it's in reference who we know as Bowser Jr. I've always found it weird that his siblings would refer to him as 'Junior', when Morton also has that in his name. And it's not as though they address their father by his name. So, the youngest child is addressed here only by his first name.
Secondly, the order used here is the order used in New Super Mario Bros. Wii, but with only one battle with the aforementioned Koopa.
Lastly, obvious as it is, these are not my characters. They belong to Nintendo.

How long has it been?
Much too long. Princess, let's go.
Brothers and sister.

We'll go on ahead.
Larry, please do be careful.
I don't want you hurt.

Brother, this can't be...
Have those plumbers no mercy?
You will be avenged.

Leaving another,
Your great strength is not enough...
Roy, please use your head.

Now two have fallen.
Mario and Luigi,
I can't forgive you!

You, the smallest one,
But with your strong heart, Lemmy,
Are next to face him.

This is not a game.
How can they not know this now,
My little brother?

Yes, two shall be left.
Sister and youngest brother,
May you both fight well.

Wendy, my sister.
I'm sorry that you are hurt.
Please... do not die now!

Bowser, though so young,
There is nothing I can do,
I am so sorry...

Iggy, calm yourself!
You must have a level head,
Please, do your best now.

Should we have left you,
When your mind was not stable?
Please, you must heal! Now!

Only we remain.
Give it your all. This you must.
Morton... Please be safe.

Oh, how could you fall?
Those brothers will not live now!
They have hurt you all!

Larry, Morton, Roy,
Lemmy, Iggy Bowser and
Wendy, I love you...

How could I stand here?
What kind of brother am I?
But, it is not done...!

I am the oldest!
I will not accept defeat!
Come to me, plumbers!

Oh? You come alone?
Yet I will not go easy.
Mario, let's fight!

Oh my god, it hurts...
Damn you, Mario! You win.
I'm sorry, father...!

I gave it my all...
I truly thought we had won...!
I failed you again.

Now that you've read this, please review. Constructive criticism is greatly desired. Please, though, no flames.