Kaguya specifically had Kazuki not use a condom the night of her birthday. Throughout the light novel, and especially after the loss of Stella, she was adamant about bearing Kazuki's child. Mio herself wanted Kazuki's child (I'll have to look up which volume she says it but I can confirm off tbat that she does say so).
The last illustration of volume 14 shows Mio and Kaguya with hands on their stomachs. Yes, those two at least are pregnant. As for the others? We're not told or shown but it can be implied that they are due to fact that Mio and Kagura are written as acting as the 'representatives for all involved'. Are Lotte and and Koyuki pregnant? Couldn't tell you. Again, It's implied. Hikaru, she's been doing it Kazuki left and right and did it againwith him in her epilogue chapter in the shower. Not shown but implied. So, take that as you will.
If you have an issue as to how Kazuki will find the funds to raise the kids? I don't want to speculate that. Too much headache.