First suggestion: Don't estimate. Get a cheap postal scale and weigh everything. I use a tenth of an ounce precision.

Since you have a hiking partner, a lot of that gear seems shared (filter, stove, tent...) so you really need to figure out exactly what is in each pack with the exact weights.

I am not sure about the climate of where/when you will be hiking. This is important when looking at shelter, sleeping gear, and extra clothing. It may be possible to shed some significant weight here.

A gallon of water does seem quite excessive, but just like my previous comment, the geography might require it.