This is all conjecture, but there's this week before the birthday. If DPC can accelerate just a little, maybe in episode 8 we will see what's up with the letter. This if episode 6 and 7 continue the story for 2 or 3 days. If for some crazy reason, episode 6 go for the entire week (doubt it), then, episode 7.
The Bella part i could see, and about Jill and Sage. I can see both ways.
Jill has a good head or her soulders, she could do something for the MC, but just for the two of them, but think it would be better to go slow with the "meeting the parents" part. At the same time she could go just as a friend, because she likes spending time with the MC.
Sage there's the possibility that her "Chad' problem would be resolved before that. Aside from it, she is being really sweet with MCs on her path, so i could see her wanting to go just to stay with him in his birthday.