I have some japanese text which appears as a dialogue caption/script for a BDSM drawing depicting a large futanari mother sitting on a couch with her son on her lap. In the drawing, the son is crying and dressed like a little girl, and the mother is assfucking him with her huge cock, when the little sister walks in on them. I will provide you the text line by line so that we can translate it into english. Make sure the translation for each line is well localized and makes sense in the BDSM / gentle-femdom context of the image. It doesn't need to be a one-to-one translation with the original, but should read well to an english audience and retain the lewd and explicit tone of the source material. Note also (in case it helps disambiguate the text) that the mother is a futanari, and therefore has a huge cock and no pussy.

Here is the translation I have so far:

Brother: "Ugh, Mom, your huge cock is really hurting me... Ah, please stop, Mom, I can't take it anymore..."
Mother: "Ah, ah, what's the matter, son? You're not supposed to make noise when I'm fucking you from behind."
Brother: "Wait, the door's opening! NAME_1's gonna see us!"
Mother: "Huh? Oh, I forgot to lock the door. I really should've remembered."
NAME_1: "Oh, Mom, what are you doing? Brother, why are you dressed like a cute girl, and making those cute noises..."
Brother: "Wait, wait, this is... Ah, Mom, why are you pushing it in so hard! I can't take it anymore!"

And here are the next lines to translate

母「ふう、ふう、ユキ、びっくりさせてごめんね、お母さん今、お兄ちゃん使って
　　性欲処理っていうのをしてるの。細かいことはあとで説明してあげるけど、
　　今は、そうねえ、お兄ちゃんはお母さんのおちんちんを入れるための道具ってこと
　　ちょうどいい機会だし、明日からユキもお兄ちゃんのこと使っていいわよ」
妹「どうぐ・・・」