Natasha is not really herself right now, so there are bound to be two different reactions for poor James. I promise, the real Nat will be confused about the situation (because she is having trouble contemplating having a kid with Steve- no offense, Steve!), but she will also kind of love the idea of having a son.
At the same time, there's gonna be conflict. So let's just enjoy the drama together.
The Doctor will love him! Because she's protective of broken children.
Harry will probably befriend him quickly over trauma.
Enojlras doesn't care because he's too wrapped up in the confusion of this world right now. Sorry!