Fusion
The Lio family's methods were already excellent.
While the age limit of humans was 100 years, the age limit of beasts was the exact same. If they weren't, then wouldn't that mean that these families could just send any Eighth Dimensional beasts they had in? They had obviously planned for this long ago. Just looking at the beasts, it was clear that they wouldn't be able to live much longer than another two or three years, a price paid for such fast improvement, which was also likely why they hadn't used such methods on humans.
As for the Gemin family, they paired themselves quite oddly.
Usually, the Gemin family geniuses would be born in pairs. When their women released eggs, their special Bloodlines, once said egg was fertilized, would cause them to split into a Yin and a Yang. This would produce twins that were almost identical in every aspect, but not quite identical.