Hello! I think I can be helpful
I can suggest you what lens bring, but for me is better to tell you what you will see, so you can decide yourself (with more experience)
In the first part of your trip, so to the lake of Varese,Como or Garda, you will see little towns facing to the lake. Looking to the lake instead, you will see also the other bank of the lake, and in some lakes there are also little islands in the middle (so I think that the 50-135 will be perfect).
For what concern Venice, as said by previous user, you will find very little street, so you don't need a wide, but something like the 50, in order to search the particular (like the river under the bridge, boats to the piers...).
If I can make you an advice, when in Venice, don't follow the crowd, but go in streets where there is noone. Most of the time you will find best backgrounds.
If you want I can linked to you some pics of internet in order to let you see what I've write (since I know that I'm not so good to explain
)