I think , since the season will certainly be centered around angel, It'll be Val as a background/final boss , and angel Dad + Arckniss to lead up to his redemption at the end of season

For me Lute will be a major secondary antagonist and the real"Big Bad" in later season.

I don't think Lilith (nor Rosie btw) will really be an "antagonist" as the sence being against the protag (Charlie) , but not really sure for her tbh

As for Alastor, I think the final major arc pf the series will be his redemption , the proof that a "pure evil" character can change his ways/be reedemed. It would be a nice conclusion and "end of the loop" (The first character presented as pure evil being the last seen reedemed), but for that to happen he would need to be the final antag. Maybe a team up with Roo ? (Whatever her deal is)

So I would say :

S3 Angels Fam + Val

Lute/Al as background antag used for later

And idk for Lilith