How do I get Mario and Luigi inside of Peach's castle in the game Mario & Luigi Bowser's Inside Story?

I'm not talking about outside the castle where there's the grasslands with the grey moles and the big green robots. I'm talking about the same way how Bowser got inside of Peach's castle with the other enemies in it. I think I remember entering Mario and Luigi inside the castle but I forgot how to. I really need help on this one and I'll give points if I get a correct answer.How do I get Mario and Luigi inside of Peach's castle in the game Mario %26amp; Luigi Bowser's Inside Story?
question. have you sen the vent where you reach the doors of the castle and you can't get in so you have to go through the back if yes then look below if not than maybe the link will help to explain better.

ok assuming you're at the entrance already just go to the left. there should be two statues on the left side. go to the bottom far left side and jump on the platform. then when you cross it, go to far up and then to the left. there should be a pink outlined passageway. go through there.and keep going up until you reach some pink tall things surrounded by moles.. go up and reach a gray platform jump on there and move ahead

you should now see orange platforms with a mushroom face. go up and you should be face to face with a wall. to the left may look closed but its not. go to the left and you'll see a blue floor with a mushroom face. go forward and you'll face one of fawful's minions. so be prepared