Yes, you should expect some questions just to confirm your application. If your husband is coming through with you, it shouldn't be any big deal. But we went through alone and it wasn't a huge thing. They may ask things like where you will be living, what your husband does for work, will you be working/what you do. Since you have your children with you, I would recommend having the signed letters from your ex in your carry-ons just in case (assuming they returned those with your app...if not...probably no big thing). The questions aren't that hard, just a 2nd check if you will that you are legit. And get used to answering them...I get them every time I come and go into the UK. Now I even get questioned when I go back to the US.
In terms of which line, that will depend. They sometimes have a line at least at Terminal 3 for those holding UK resident visas...if it is open you are lucky. Last time I came through we were on one of the first flights of the day and it wasn't (but we got to go to the front of the line anyway because I had my 2 yo with me). Sometimes if you are traveling with your spouse they will let you in the UK line (but rarely). Even if you have to go through the regular line though no biggy just a long wait.