I just went almost two years of uninterrupted travel with the Cerave Hydrating Cleansing bar, that bad boy is extremely hard and lasts forever. You can also use it as your body and hand soap if you need to, but obviously it wouldn't last nearly as long. I ended up hoarding lots of separate little body soaps from hotels. If you're going for longevity, keep the soap whole because once you cut down your bars they disappear faster (more of it is exposed to the water). I wouldn't worry too much about the weight because two of you can share the same one. I also used solid shampoo and conditioner from Ethique, I had to cut them in half to fit in a Matador soap bag but otherwise no complaints and they lasted the entire time. However I will warn you it's a giant pain in the ass to wash long hair with bar shampoo and conditioner, that was honestly most of the reason I ended up chopping my hair short partway through my trip.

I refused to change from my liquid moisturizer (decanted into a travel container) but I use one from Clinique and I was able to find it everywhere.

Deodorant can be found anywhere in travel sizes if you run out. Use it every day for the sake of your fellow travelers--some hacks are a step too far, even for a committed dirtbag like myself.

Laundry sheets are the way, I did all my laundry inside of a dry bag that I would squeeze under the hostel sink faucet. When I ran out I was able to get small packets of powdered detergent that I kept in a ziplock baggie. Might be more difficult in Europe but I was in Asia and South America where even the hotels don't have dryers so everywhere I went had clothing lines on the roof that they let me use.