The only thing that would make sense is if he has more than 1 sis...
I was confused too! If he has two sisters, why can't she babysit them more often so he can take a break? Custody could still be his, but she could help bear the burden with him. That particular part of the story was not well thought out by the mangaka.
I agree with did she not get custody or why does she not help with them more. The author should have made 1 more chapter telling about how he got custody
You are aware the seme's sister is dead? This was the uke's sister. You're welcome.
You do realize that the twins were the uke's dead sister's kids? And the sister shown was also uke's sister. Hence the confusion.
The last story, I thought the sister is dead????