The skill rounds carry over when evolving, even when the active changes.
The broken statue maxes out at skill 10; the evolved one (and Minamoto) at skill 12.
If you only evolve one maxed statue and feed it to Minamoto, the result will be skill 10 Minamoto at minimum; any skill rounds he already has will be retained, and if that's enough to get him to skill 11 it will. There's also the chance that skill level jumps when feeding cards with the same active; that happens after the manual adding of skill rounds, so if he had enough rounds to get to 11 then a lucky up would push it to 12.
Pontos 5* maxes out at skill 10, so you only need enough rounds to get to skill 10. Conveniently the 2* Nymph maxes out at skill 10 as well, so you just need to max one of those and feed it to Pontos 5*.
Pontos 6* unfortunately has 12 skill levels, so you'd need either two Harpies or a second skill 10 Pontos to feed in.