Facing so many loses and changes would affect any one, it understandable you would be feeling bad. That being said, there are a lot of things you can do, others have made good suggestions. Here is my suggestions. First, take a deep breath. In stressful situations, take a moment to recharge your brain. A quick simple way to calm yourself: close your eyes, breath in slowly through your nose for a count of seven, hold your breath for a count of seven, then breath slowly out through your mouth for a count of seven. Do this seven times, you will be amazed how much calmer you will feel. Repeat as needed.
Since you are struggling with your marriage/sex life, I am going to make a suggestion that you and your wife have a date night each week. Date night doesn't mean you have to go out, but it does mean you make your relationship with your wife a priority. Let the kids spend the night with friends, and prepare a nice meal for yourselves. Take time to to talk, go for a walk, or for coffee, or watch a movie. At first, don't use the time for sex, but to rekindle the romance, and improve communication. In times of stress, it may be easier to draw away and just think of yourself, but resist that, you guys need to work together to find solutions to your problems. Brainstorm together to think of what to do about your child issues. My husband and I do this every Friday. We are empty nesters (kids all grown), but it we still think it is important, and we don't need to get drunk to have sex. I heard recently that men who do household chores get more sex, so give that a try. You have lost so many other things, don't loose each other, that will only make your life worse.
Your kids: If they are acting up it may be because they are confused and also dealing with with these changes in their lives. Take one at a time and go for a walk or do something they like at least once a week. Don't make a big deal about it, just do it. Find something you can share with just the two of you.
Money issues, do a budget, you will never improve your financial situation without a good budget. Work with your wife (not on date night though, lol) to come up with a realistic budget. Allow some money for fun, and talk to the kids about what things they can give up and what they can't. Children are smarter than you think and will usually be more understanding if they know what's what. You may think you are protecting them by not talking about it, but they probably already know.
Focus on the good. In times of trouble, keep thinking about what you do have, not what you don't. You have your health and two healthy, if wild, kids and a nice wife, there are a lot of people who would gladly trade places with you. Do what you can to improve your situation, but do not forget to be thankful for what you do have. I have fairly serious health issues, but I get up each day, grateful that I am on the right side of the turf. In the past I focused on what I didn't have, now I look back and realize I just made myself miserable for no good reason. I have my bad days, who doesn't? But I don't let it take over my life. When you start feeling sorry for yourself, go buy a cup of coffee for the bum on the corner, and think about how nice it is to be the giver in that situation.
I hope things get better for you, I find if you wait long enough they usually do.