All three parts (time skip, prengancy, and the war system) are not made yet and therefore everything I talk about might still be changed by the time it gets done.
The time skip will happen in multiple steps, but without specifying the exact amount of time that has passed for each step.
I currently imagine to do the time skip on a special world map, where you can select icons to view events that take place at that time, before you advance to the next phase with something like a "turn end" button.
First phase might be about preparations for war, and the selection of a bride (or harem route with multiple wives), then you'd get a phase about war with other countries (if you declare war on someone) and training with Varea/Frall/others?. Then we could have events with pregnant characters, about your children being born, and later about how (some) have grown, all while the preparations for the war against Raziel still continue.
The children are not planned to be all born at the same time, so they'll have different ages at the end. Additionally to the difference their races will cause.
I wouldn't agree with your statement that having a child with a woman „enslaves“ them. ;) But obviously choices you made during the pre-time skip events will in some way be of more or less importance. As mentioned above, the war against countries will be before the war against Raziel.
[There are channels on the Renryuu discord server specifically for the discussion about war, politics, Ryen's future family, and more.]