Marisa,
Blending families is not an easy task. I know this from working with many clients who are from or who have created a blended family, as well as from personal experience. Just the work you have done as a family-- is great.
The real problem here is you and Joe. Outside of all your other external stressors such as lack of family support etc. You and Joe have to work on the strength of your relationship as a couple first. WIthout it--those two beautiful girls will have no foundation to stand on.
You have to make decisions as adults and stick to them. THere is no "outside" force making you argue in front of the kids. It only takes one person to calm the situation and say "let's talk about this when the kids go to sleep, or go outside to play, or if necessary in another room with the door closed and some music in the background."
What do you and joe argue about? Money? Family? Sex? Whatever the issues, make the choice (and joe has to make it too) that the problems will only be between you and him. ANd solved between you and him.
If you'd like to talk further you can visit me at:
GirlShrink.com <img src="/images/graemlins/smile.gif" alt="" />