OK, here’s what I’d rewrite:

To their two friends, the treehouse was more than just a treehouse. It was a sanctuary away from the other kids, where they could be themselves without being teased or bullied. It was their secret fortress, hidden high in the branches of a huge oak that only they knew existed. At least, that’s what they thought. They were more than a little annoyed when their two younger sisters decided to turn the treehouse into a princess castle by painting the inside pink and putting glitter everywhere.
assistant
The sentences in this paragraph need some minor editing and punctuation corrections. Here is a revised version:

To their two friends, the tree house was much more than just a tree house. It was a sanctuary away from the other kids, where they could be themselves without being teased or bullied. It was their secret fortress, hidden high in the branches of a huge oak tree, which only they knew existed. At least, that is what they thought. They were more than a little annoyed when their younger sisters decided to turn the tree house into a princess castle, by painting the inside pink, and putting glitter everywhere.
assistant
Will you help me fix all of the errors and mistakes in this text?

To the two frien57354ds,    the    trehouse   was   much more then a treehouze. It waz @ sanctuary aw@y fr0m da other kidz wh9Ere they could be themse$*#@lvez wifout being teased or bulied. It was their   seecret fortresss hiden high in   the bran&%$ches of a huge oak that only they knew exizted. At lea#%#st that is wh%#%at they thou%#%#ght. They wer$%#e more than a little annoyed when their two yunger    sistErz   decided to turn the   treehoue into a   princes castle by painnting the iinside p%#ink an352d puttting gliter everyw%$%#here.
user