Yeah, like Elissa said, planning later in the year would the safest bet if you really want those two rides. I booked my trip to CW for October based partially on the uncertainly around AlpenFury's opening date. If it's any consolation, CP's website does say that that Siren's Curse is scheduled to open "early summer" and with the track work being (edit: nearly done) I see no reason to doubt that (barring any sort of TT2-esque nonsense). Remember that the new "Six Flags" parent company is like 99% old Cedar Fair employees and Rapterra was good to go at King's Dominion on their opening day 3 weeks ago.
And yes, the "legacy" CF parks all have separate phone apps, and you need to log into each separately. It's been so long since I've done it I can't recall if its a single account/login (I'm pretty sure it is but I could be wrong) or if you need to load your pass in to each one separately.
Is your pass purchased from a SF park with the All-Park add on, or from a CF park with the All-Park add on?
I bought my pass with the add on through a CF park, and when I load it into the SF app it doesn't show up as an actual season pass, but rather a "Gold Pass Daily Ticket" that doesn't expire. Not sure if that would work the other way around too.