Yeah I got it so far, however I thought at the point everyone thought he was her biological son was because the (step)father was human, where he got his human looks to naturally eventually go through furry-puberty/transformationMC is half human half wolf-furry.
Wolf stepmom became barren after complications during childbirth (giving birth to wolf stepsister).
Wolf stepmom then adopted two babies: a boy (MC) and a girl (cow step-sister).
Cow sister is very visibly adopted.
Mom did not tell anyone that MC is also adopted
because MC race happened to match well enough that it was not immediately visible he is adopted.
Everyone thought he was her biological son.
Shortly after the game start you discover that you too are also adopted.
In summary: you have a step mom, 2 step sisters, and several biological sisters who are being introduced as well now that you discover you are adopted.
The point that doesn't seem clear is if he's actually a "wolf" hybrid, since as of 0.4 release there's nothing to confirm what his other half is unless I missed it, since, as far as I know, there's no signs pointing towards one of his real parents being a wolf yet
That is, unless I've missed something outside the story that the developer has written, of course, like a "they adopted him BECAUSE he had wolf genes in him", but that doesn't seem quite in line considering one of the moms lines, as she had just seen MC the first time at an orphanage was "even when they told me that you were a (unspecified) half-breed and the dominant gene simply had not manifested itself"
So it seems like it was news at the time for the mother as well
Not saying that it isn't likely it'll be the case in the future (cause wolves are cool and all) I'm just pointing out that it doesn't seem to be explicitly stated