How would the harem members react if they found out they were pregnant with the Reader's child?
Because there are so many harem members, I will do the ones who I think will have a bigger reaction or are deemed more important in the publics eyes. If I don't end up writing about a specific individual that you wanted, please let me know!
One TW: In kaeya's there is a mention of miscarriage.
Diluc is expected by most of the court and the public to bear the first heir, which in other words has to be a female. I do think that he will be the one who gives birth to the heir even if there are a few... hiccups along the way. I also think that he would probably want to have a few children. Three at most. Part of this is due to his family's training and it being ingrained in him that he needs to give you children. However, I do think he does genuinely love his children (and the other harem members' children) and after the first birth he wants to have a few more but it was his choice.
As for when he found out that he was first pregnant, there are different reactions for different scenarios. However, overall he doesn't mind being pregnant, espeically not when it gives him a chance to be spoiled by you.
If he was the first in the harem to get pregnant, he would have a lot of anxiety and nerves. I imagine that the public and the council and court members would want to celebrate and make it a big show to the public. Something Diluc would feel highly uncomfortable about but he would also feel obligated to do as they say. Though you would shut it down the second you saw that it was doing more harm than good. However, with the support of you and some of the other harem members, he would enjoy his pregnancy, despite the discomfort and pain.
If other members of the harem already had children, there would still be anxiety, but there would also be a lot more pressure on him by others (court officials, etc) for him to have a male so that his child can be heir. This route could easily lead to him breaking down because of sheer pressure and he would probably let it build up without telling anyone until it all hits a breaking point. However, he would handle the pregnancy itself realtively well.
Ayato is an odd case. I do see him wanting children but not many, probably no more than one. Besides, he knows that with his position as Noble Consort it is expected of him to at least provide spares, so to speak. He is fine with this, he doesn't hate it but he doesn't love it either. When he first finds out he is pregnant, he is resigned. I imagine him and Reader already planned for him to have one so he knew it was coming up. I will say he was one of the ones who milked all the care and attention from reader while pregnant. If he is going to suffer through an uncomfortable pregnancy, he see's no shame in making sure he is heavily cared for.
However, he is relatively good with the children too because he grew up with a sibling of his own and the two of them had a very good relationship. With this in mind, I do see him considering having another child but then once the other harem members start having children of their own, he see's that it is not necessary for him to provide another.
Aether is the very serene with his pregnancies. It may have to do with the fact that he has the easiest pregnacies and births out of all of the harem members. In my mind, he takes the idea of 'glowing' to a whole other level. He is perfectly content throughout the whole process, taking everything with grace that leaves others wondering how he is functioning. However, once he finds out, I do think it would take a while for it to set in that he is pregnant.
Ajax wants a lot of children of his own. He grew up in a large family and despite the struggles they faced, he loved his siblings deeply. However, I don't imagine him being happy while he's pregnant. He is estatic at the idea of having his own children but he hates the way it affects his body. It makes him bed bound and lathargic and he can't move around or fight which leaves him uncomfortable and bit tense when others are around him. It is best to keep him separate from a few of the other more testy harem members.
Itto is estatic from the moment he finds out. While his pregnancy may be a bit rough towards the end due to his different body shape compared to the others in the harem, he hardly feels the pain. He is always looking for a bump and he is one of the members who is very comfortable with letting others feel it as well. He almost always has a hand on his stomach once it becomes more prominent. If he could, he'd love to build his own little army of his children.
Scaramouche would be one of the individuals who gets sick when he first finds out, his nerves working on overdrive, anxiety at an all time high. By the time he does come with child, I imagine there are plenty of children already born so he is more comfortable with the idea but there are lingering, unresolved doubts in the back of his mind. He secludes himself in the beginning, feigning that he is sick or unwell but not telling anyone. He wouldn't tell anyone but eventually someone (other harem members, servants, someone) would find out and would alert you. It is only after a few months and support from those around him (this is, in my mind, years after he joins so he is not as hostile or closed off anymore) would he become more comfortable and even excited. He handles the pain remarkably well.
Kaeya is a unique case when it comes to his first child. If he is still struggling between his loyalty to the reader and his family, he would, in simple words, detest being pregnant because his mind is riddled with anxieties: his family would try to use the child as a barganing chip, something to raise their own standing. He doesn't want to subject a child to that and honestly, he'd be so torn it wouldn't be surprised if he miscarried. However, if it is years later when he is not as heavily bound to his family, he would still feel a bit anxious about learning he is pregnant but he'd be less anxious and a bit more calm throughout the pregnancy.
Really wants children of their own:
Diluc
Aether
Ajax
Itto
Kaveh (really wants at least one but he is very hesitant to ask because by he is a bit older than most of the other harem members and the public considers him past the proper age)
Doesn't particularly care either way. Isn't a fan of the pregnancy itself but will love their children.
Ayato
Albedo
Thoma (Is adored by all the harem members' children but is in no rush to be pregnant himself. He is perfectly fine helping the other members with their children but would not be aversed to having his own)
On the fence, or, in other words, may not want one when they're younger but may be more open once they get older.
Scaramouche
Kazuha
Kaeya
Heizou
Gorou
Zhongli fits here as well. He may not be a harem member offically but he has fanacized about having a child with you. But he is hesitant because he never wants to be put in a position where he cannot be your knight or feel like he cannot protect you.
Absoultely does not want children of their own:
Al-Haitham
Xiao
Venti