From the looks of this comic and the previous one like it with Reimus, I'm assuming the food they're forced to eat is some sorta of fibre.
So they're not allowed to shit and are foced to eat fibre. Looks like the yukkuris are in another paradox. What will they do? Get pissed at each other of course!
They only get pissed off by each other because they're Marisa types. They're very selfish, since the kids don't wanna hold their poopoo they let it out.
1) Reimu types have a strong sense of empathy, and perhaps because of that they have strong self-control[or endurance, or tolerance of unpleasantness or patience]. .... [I'll do the text for the black parts later]
2)Top to bottom Yufuu... yufuu... It's all dry and not tasty*... Yu uu uu... I want to drink* water*... mu-nch mu-nch...
3)R to L We don't* need this much* bad tasting* stuff*!! Marisha's* stomach is already full! I don't wanna wait to poo poo!!
4) Big M: YU" AA" AA" AA"!!? What are you selfishly doingggg"!!! Right M: I can't* wait anymore! I'm going* to poo poo yukkuri! Right M: Refreshed-*! Mid M: Marisha's* poo poo is coming out* too! Mid M: Refreshed-*!
5) R to L Marisha* was holding* poo poo in, and it was really* painful*! *pukuu* [*puff*] Understand* that yukkuri* at least* okay!
6) R to L Mommie is feeling the same!!! I told you if you're found doing poo poo onii-san will kill you didn't Iiii!!! How many times do I have to say it before you understandddd"!?