I wouldn't want to hazard too much of a guess as to how much longer of a wait you have, but I think you have a reasonable chance of DM by mid-March.
You can cross the border at the same time with your husband and children. I don't know where you found information that says you can't cross with them, but it's not correct. My wife and I have crossed together several times in both directions over the past year. Unless there's something in your background check that's causing CBSA a concern, you shouldn't have any big problems. You might be pulled into secondary, so have your husband's sponsor approval letter, as well as any other correspondence you've received from CIC.
If asked, explain that you know you're just visiting, and you understand that you'll have to go back to the US if you don't have PR. In most cases, CBSA merely wants to see that you understand the rules, and you're not trying to go around them.
Unless you get an agent having a bad day, but that's a whole different story...