We know humans and tsugumomo can have children together. We also know that Ouhi's mother was the tsugumomo parent. That means we know for certain that tsugumomo can get pregnant. It definitely stands to reason that they could breed among themselves.
We also know that Ouhi and Ouna inherited...
I'm assuming the random "mother" on page 25 was "haha", which is probably intended as gasps for breath, not Mikazuchi calling for her mom for no apparent reason.
I know I'm 4 and a half years late to this, but it's a crossover with a manga called Kakuen no Hinagiku. I don't think there are any translations of it still, but I found this mega upload of the raws.