We thought it was pretty clear but then we do this sort of thing all the time. If you had never caught on that we were both involved in this then you are not quite as clever as you thought.
So here you are this is the final answer to the riddle (plus a little extra of my own)
1) There were 2 "Snapes" at Hogwarts in 1991/1992. Severus and Louisa.
2) One of them was a Riddle.
3) There are seven bottles: 3 are poison, 2 are wine, 1 lets you forwards, the other sends you back-wards.
4) The largest and smallest of the bottles are NOT poison (2 & 6) so they contain wine.
5) Poison is always on the left of wine (1 & 5).
6) 1 & 7 are different but don’t help you go forwards so it must take you backwards.
7) By process of elimination 3 moves you forwards and 4 is poison.
There is only one problem that I had when I found out that Professor Quirrell had gotten to the bottles first and that was. What if he had mixed them up in some way? What if he had switched them in case someone had arrived after him. My logic was always what if he needed the potion to get back.