From what I know (and I'm the webmaster, so take my advice with a pinch of salt) I would say that the one that is turning yellowish in the middle IS starting to involute. That is the classic sign. And, no, 8 weeks is not too early for involution... every hemangioma is individual.
For the other, turning blackish with yellow scabbing... could you post a picture, by chance? That one sounds like it might be beginning to ulcerate, but again... what do I know?? If you could post a photo of that, you'd get better feedback from parents who have experience with that very thing.
If you have any troubles posting photos, send one to email@example.com
and I'll post it to this thread for you.
Parents with experience in this will chime in very soon!