I'm doing kitchen renovation and want to remove a few walls. Those are on the first floor of a 2 story house(no basement).
I've opened a few of them and did my best to provide all the pictures.
I opened the ceiling and checked how joists run above those walls. Looks like they just run through them a few feet past the walls I'm considering to remove. 

1&2 is a small closet. 3&4 is has only 1 wire inside which is going into the slab.
the niche between those walls was supposed to be a built in desk

[![enter image description here][1]][1]

[![enter image description here][2]][2]

[![enter image description here][3]][3]

[![enter image description here][4]][4]

[![enter image description here][5]][5]

 1. Can I remove them (Wall 1,2,3,4) and make the back wall flush?
 2. Should I reinforce those joists? For example I can do sistering with a plywood from both sides of them.

Edit:

[![enter image description here][6]][6]

Wall 1/2 Intersection with trusses:

[![enter image description here][7]][7]

[![enter image description here][8]][8]


  [1]: https://i.sstatic.net/Id5Kz.jpg
  [2]: https://i.sstatic.net/Ru8Bz.jpg
  [3]: https://i.sstatic.net/1lb5y.jpg
  [4]: https://i.sstatic.net/be6QV.jpg
  [5]: https://i.sstatic.net/FgOlz.jpg
  [6]: https://i.sstatic.net/OLz0x.jpg
  [7]: https://i.sstatic.net/sQq6z.jpg
  [8]: https://i.sstatic.net/zzeT9.jpg