The RNG correlation for Colosseum starters is more than just PIDIV. When the game generates your trainer data, it also generates your starters, so the starters have a correlation with the TID/SID. It's not permitted for an "arbitrary TID/SID combo"; a given TID/SID combo must have a corresponding PIDIV for both starters, and the starters must generate as antishiny with fixed gender, so it's not a "7 frames later". If the starter ends up shiny or the wrong gender, it will re-roll the PID until it is correct.
The only seed that gives you your desired TID/SID is 0x3074D719.
Span<uint> seeds = stackalloc uint[4];
var count = XDRNG.GetSeeds(seeds, (34625u << 16) | 64821u);
seeds = seeds[..count];
seeds.Dump();
With that seed, the resulting Umbreon is: PID: 391A8655
Umbreon (M)
IVs: 3 HP / 10 Atk / 17 Def / 22 SpA / 23 SpD / 13 Spe
Ability: Synchronize
Level: 26
Serious Nature
- Bite
- Taunt
- Secret Power
- Snatch
And Espeon is: 0x81DDDE59
Espeon (M)
IVs: 13 HP / 10 Atk / 2 Def / 9 SpA / 11 SpD / 0 Spe
Ability: Synchronize
Level: 25
Mild Nature
- Confusion
- Return
- Reflect
- Helping Hand