I certainly understand your frustration because that's exactly where I was a month ago. When I first got my system with its XL cups and this very tiny length of tubing to the Y connector; that first day, I managed to get both on seal for about 10 seconds after an hour of trials.
Thankfully, I had been reading the forums alot and seen others having similar issues (usually when they went up to a new cup size). So as you have, I just noogled with one at a time. It was so frustrating and of course I felt "if I was only bigger" would fix everything. Then the skin issues started up and then I kept hurting myself, etc. There were times I was ready to scream and throw it away.
But you know, I wanted breasts so bad that I was ready to endure that frustration and pay the time and effort to get this silly little torture device to work.
I hope you feel the same way because it *will* pay off. Why? About 2 weeks into just noogling singly, I began really trying to develop the motor skills needed to position, hold and pump with both. Then a small miracle happen, I found I *could* do both after noogling singly for about 10 minutes. It gave me that extra skin to "latch on" with both. It wasn't until last week where I could just place, hold, and pump without any effort (and it isn't every time -- I still use those skills).
And I haven't even talked about the frustration of that little tubing, cup sliding and only being able to noogle both by being off center since I didn't have any skin to grab there. I am happy to report I am conquering those issues too.
I know it is frustrating because I think you want to improve your breasts so much. This is a good thing as it will sustain your efforts but this is new skill and you'll likely be doing this activity for a year (or more). So it is perfectly fine to start slow, develop the skills and experience to arrive eventually someday you too will wonder "why was it so hard?".
Just be open, experimental, and do lots of reading. There are plenty of long threads full of success and trials as things went wrong. I have found these threads most fruitful because it "looks" easy but I soon found it is not which nice to know since I had a very rocky start.
You can do this -- practice... practice... practice!
DJ