It is very hard to give advice in a vacuum -- that is, I'm sure there are lots of circumstances that need to be considered before making a big move. Through my blog, I am offering my opinions born through experience. Moreover, I am a coach not a counselor. The difference is that a coach believes you know the answers to your questions, and I may ask you powerful questions that help you to bring to the forefront what you know to be true. That said, in this note I will offer you only some thoughts on the subject.
There are two schools of thought on moving out of the family home after a death in the family. Of course, if affordability is an issue, you may not have a choice. However, if you have the luxury of deciding whether to keep the old house or move somewhere new, consider that there have been many changes in both your life and your children's. Change and not knowing what the future will bring often causes a fearful reaction. And, it is from this fear that negative behavior may erupt (such as not getting good grades, not helping around the house, etc). Children need to have constants in their lives and changing schools can be another traumatic event to handle. On the other hand, you and your children might enjoy a fresh start where you don't feel burdened by your "story of loss where your children might feel they are being pitied, etc.
I think children can be influenced to see a move as a good thing or a bad thing. They will always follow your lead. If you make a move to a new city an adventure that will be exciting, then they can come to see it that way too.
You might also look at your behavior as you grieve. Is it possible that you have let the housework go, etc. This is quite understandable, but your girls might see you do this and so they follow suit by not helping around the house. Again, these are just some ideas and I suggest you go see a counselor in your city to help you sort things out.