>>719235007
For the parents, I used the 3 star stamina golshi I had laying around as one of the grandparents (who happened to also have 2* long sparks), then borrowed in a grandparent that also had 3 star stam and long sparks.
Then the parent born of those two wound up with 2* stam sparks, giving me 8* stam sparks on that parent and mostly long but also one pace-chaser pink spark which I'm okay with (pace-chaser S would only race wit, ideally that should be more long sparks/turf, as distance in S is the most important, but having S in terrain type helps with acceleration. S in style isnt that important so you can avoid that unless you're trying to raise the aptitude of say a B end closer to A end closer, then you want end closer sparks.
Anyhow that's how I did it. You can reuse the same 3* grandparent you did for one parent on the other so long as the affinities are fine. Use the affinity calculator to plan out which characters are going to guarantee you double circle affinity by the end of it.
https://gametora.com/umamusume/compatibility
Then if you wanna get fancy you can train up the grandparents/parents with a special deck that has ability hints for skills you want the child to inherit. Asides from that, have your grandparents/parents win as many G1s as possible, as that will lead to better affinity and more sparks. The best white spark you can get is Ura Finale, and you get it randomly after completing the finale. So you want them to finish their career. I'd say aim for 2* sparks on the parents for now. Getting 3* takes a while and you can breed up a faster parent that way. If you dont have any 3* sparks yet to use as grandparents, just use a 2* until you can upgrade them.