One potential antagonist could be Lucifer's father. He might not approve of the union or the baby, seeing it as a disruption to his grand plans or as something that could change Lucifer in a way he doesn't want. Another could be some of the demons from Hell who see the baby as a potential threat to their power or existence if it has some sort of unique abilities.
Dan would probably be shocked at first. He has a complex relationship with both Lucifer and Chloe. But he would also be concerned for Chloe's well - being and the future of the baby. He might offer his help in more practical ways, like making sure Chloe is safe during her detective work. Ella would be super excited. She's always positive and would probably start knitting baby clothes right away and be full of ideas for baby names.
Maybe the pregnancy is unexpected, and they initially panic. But then they start to get excited about building a family together. Chloe could start to train Lucifer on how to be a good father, like teaching him about baby care and normal family values, which would be a big change for him since he's from Hell.
Chloe Decker's dad doesn't die in the comics. The storylines don't include that event. Maybe there's some confusion with a different version or interpretation, but in the original comics, he remains alive throughout.
Their friends would probably be really happy. Amenadiel might be a bit surprised at first but then very supportive, seeing how much Lucifer has changed because of Chloe. Dan would be a bit more hesitant, but eventually come around as he sees how happy they are. Maze might be a bit jealous at first, but then she would also be happy for them as she cares about Lucifer.
One heartwarming scenario could be Lucifer finally confessing his true feelings to Chloe in a very vulnerable moment. Maybe they are on a rooftop overlooking the city, and he tells her how she has changed him for the better. Another could be when they go on a simple date, like a picnic in the park, and they just enjoy each other's company without any of the usual chaos around them. And a third could be when Chloe finally accepts Lucifer completely, including his devilish side, and they have a big embrace in the middle of a crowded room.
One idea could be that they face challenges in their relationship due to the pregnancy. Maybe Lucifer is worried about his devilish nature affecting the baby, while Chloe is trying to balance her detective work with the new situation. Another plot could involve them having to protect the unborn child from supernatural threats, as Lucifer's world is full of such things.