OK, first of all, plainly this is a mess. The fact that there is a white wire hooked up to a black wire without any recolouring of it alone says that (1) there's some amateurish stuff going on here, and (2) you cannot trust any of the white wires to actually be neutral until you prove that they are. So proceed cautiously, and take notes as you go.
There are a lot of questions here but a good one is:
What's the easiest way to track a specific wire to see how it flows without ripping out the walls?
Start by obtaining a long three-prong extension cord. Plug it into an outlet that is on, and verify with a voltmeter that there is voltage between the hot and neutral, there is voltage between the hot and ground, and no voltage between the neutral and ground. You now have an extension cord which you can use to provide a known ground and a known hot.
Next, turn off the power to everything that you're going to be working on.
Next, put a piece of tape with a number on every wire that you're going to be working on, and start making notes about the color and location of each numbered wire end, and what they're hooked up to now. Take photos. You want to be able to put this back together the way you found it later. Number the switches as well.
Next, carefully get all the wire ends exposed but not touching anything, and turn the power back on. Use your known ground and your voltmeter to determine which wires are hot under every combination of switches. Remember, some of the whites are hot.
Turn the power back off again.
Test everything again to make sure that no, really, the power is off.
Now test everything again against the known hot to find out which wires are neutrals that run back to the panel. Again, test everything against all combinations of switches, remembering that at least one mistake has been made in this wiring so far; there might be more. Interrupting a neutral with a switch is almost always wrong, but I have found plenty of interrupted neutrals in old houses.
Now unplug your extension cord from the wall and get a flashlight. Rig yourself up a continuity tester out of the extension cord and the flashlight. (Of course if your voltmeter has a continuity tester, use it instead of jury-rigging one out of a flashlight.)
Suppose you suspect that wire ends labeled 2 and 9 are the same wire. Attach end 2 to the extension cord ground. Run the extension cord to the other. Now wire the extension cord to the battery, the battery to the light, and the light to end 9. Did the light go on? Then your hypothesis is confirmed. Did it not go on? Try every combination of switches. Again, record your observations.
Keep doing that until you have enough observations to form a consistent theory of how the wiring runs through the walls. Draw a diagram.
Once you're there, you should be able to solve your problem. If you cannot, then you'll be able to post a question here with a lot more information.
Also, take this opportunity to ensure that every wire is correctly coloured, by putting tape on miscoloured or confusing wires. Also, if there are oddities such as a box that has hot wires from two different breakers, make a note of that for the next guy.
I think you want to leave the kitchen box alone and rewire the 2-gang box like this. I used blue for the white neutral wires:
I followed the color scheme of the existing wiring, with the red carrying unswitched hot in the 3-wire cables. Please remember to mark the white traveler with black tape or paint.
You can re-use the duplex you have, but you might want to buy two new three-ways. You could straighten the tabs on the abandoned one but you have to go to the store anyway.
I sent the power to the further three-way first instead of to the one in the gang box because it saves one wire-nut.
Best Answer
The key for you will be finding a double switch that has a 3 way and a one way, seeing as you want to eliminate the need for changing out your box - assumption here is that you have an existing installation with drywall already in place. There is another factor at play though - NEC CODE requirements for how many wires you can put into that existing box. - How much space - you can't just stuff more wires just because you might have a wire hole to feed them into.
However installing a bigger box is really not that hard in this situation as some newer boxes have the box mounting screws internally - not on the outside where it would be difficult to mount in an existing installation (and yes they are screws - quite nifty for about $3.00 USA).
Your wiring might look something like this below.
Below you will find an example of the SMART box by Madison Electric
In your situation this makes perfect sense to use.} The Tabs for studs - if you don't need / use them they are removable...