So, in terms of who to add pregnancy content to first, I'd either go with Kylar or the Great Hawk. Why these two? Well, Kylar is the only character who definitely wants kids with you, so it kind of makes sense to work on them. On the other hand, since they are the character who wants kids with you, they could be the most potentially time consuming to write content for. So, do you focus on getting them done, or set them aside for later since Kylar would likely be one of the most involved parents?
As for the Great Hawk, the thought process is opposite of Kylar. The Great Hawk should be one of the easiest to write pregnancy content for (in theory). First off, you'd be laying eggs for the Great Hawk. Now are you always capable of laying eggs for the Great Hawk or only when you have the bird transformation? This is up to the developer. Anywho, eggs. How long do you carry eggs? Well, I'd probably not even give them their own timer in settings, just have them take about as long as the parasites to expel. How long for the eggs to hatch? That's easy, a month or four weeks. That's how long it takes for real hawk eggs to hatch. How long until they leave the nest? Again, easy. Two months or eight weeks.
However, since the Great Hawk is the Great Hawk, maybe their children are also... great? So, if you wanted you could double or even triple the time to represent the abnormal size of the children. That would mean hatching taking two to three months, and leaving the nest taking four to six months. The eggs of the great hawk would probably be pretty big, I'd assume you'd only be able to lay one or two at a time. After the hawk babies leave the nest, maybe you can sometimes see and/or hear your children in the skies. Occasionally, they might even save you from danger.
Are the hawk children ever harpies? I'd use the beast settings to decide that. Not even a new one, but the percentage of beasts that are replaced with monster people one. I have my settings that they can appear at any time, cause I just consider my character to be in a semi-mystical world, so the occasional beast person is normal. My settings are at 1 percent, but for some reason I've seen an abnormal amount of centaurs, that might be a bug. Anywho, I have the Great Hawk set to always be a monster person, but their children would be normal hawks most of the time with my settings. Which is fine by me, I like the mystical to stay mystical. If I see them everywhere all the time, that's called being the norm. It ain't mystical, lol.
The thing to make sure of is if an egg is hatched into a harpy/hawk, it stays that way when the settings are set to at any time. It would be weird if you came to the nest and the children keep transforming back and forth between hawk and harpy. That only makes sense when using the only when hallucinating setting.
