Mind of tempest
(he/him)advocate for 5e psionics
do not remind me of Pokemon egg groups I get flashbacks I have seen horrors you would not believe.The way I would do it is split species traits in 'major' and 'minor' traits. To make a mixed race character you pick a base race and you get the major trait and then you can trade any of your minor traits for the ones from the other parents. Some major traits would be powerful and wouldn't leave a lot of room for minor traits but others would have a lot of them.
Again: Egg Groups. There's 16 of them in Pokémon and over 1000 Pokémon and they all fit in one or two of them and they just add the new ones.