Annoyed by sister in law

So my little brother and his gf are currently expecting. (They’re freaking 15 &16). She’s 12 weeks and she basically lives at my moms house now. Well since she’s became pregnant she has not helped at all with keeping the house clean. I understand my brother and her don’t have to do everything but my mom is working to feed both of their asses and the least they could do is helping her clean. Just yesterday I asked them help with dining and living room and they both flat out told me no because they didn’t make the mess.

I’m just sooo super fucking annoyed by this. Like I understand being pregnant makes us tired but it DOES not make us disabled!