Just to jump in- @Kim, if you're considering the crush/love potion ones for Cronis but don't want it to actually happen to Hit, Johnny & Margo can fail miserably, and not only that, but they will also take the fall if it ends in disaster.
For Hogsmeade, if you want to up the stakes perhaps they've been sent to collect something that can't (for whatever reason) be delivered normally to the school? Or it could be something totally normal just urgently needed. A new quill? Sweets?
@Madd- looking over Antonin's app I have a couple suggestions (if it'd help!) 1. He seems fond of magical creatures. Perhaps he's heard there's an interesting one in the Forbidden Forest and wants some company finding it? 2. An easy one- Margo is basically Hogwarts' rumour mill. With all the awful rumours floating around about Antonin perhaps he asks M&J to float some more positive ones to counteract the negativity? I have NO idea how likely he is to do either of these, just working off his app.
Literally throwing ideas around guys, feel free to disregard if they don't work at all! I cannot stress enough how happy we are for them to end up in ridiculous/dangerous/awkward situations. There is almost nothing they wouldn't at least try to do, so anything goes!