Yes it is absolutely normal to each have your own lawyer. My ex and I did mediation but we each also had our own lawyers on the side to consult with. It's important for you to know whether you're getting a fair shake. The only time it would make sense to use one lawyer is if there were no kids, no assets or debts and similar incomes.
As for telling the boys - I know lots of people advise saying it's mutual. I refused to say that as I very much still wanted my marriage at that time. But maybe in your case you'd feel more comfortable saying that? I dunno.
The most important thing is to be calm (if you're panicked they'll be panicked) and reassure them that you both love them and that their lives are going to continue (same house same school). You might be surprised, once they see how relaxed and happy the household is without him around they might quite enjoy it. And at least initially your H may play Disney dad so they might get some actual quality time with him.
You need to be their rock. Hide your stress as much as you can. Stick to the high road and don't badmouth their dad no matter what he says about you. They will respect you for it and for not putting them in the middle.
