Thank you for emailing in. It sounds like your 13-year-old is really challenging the family right now. There is a lot of growing, both emotionally and physically, that kids go through at this time in their lives. They are earning more privileges but also gaining more responsibilities, so frequently check in with him. He needs not only a very clear explanation of what your expectations are but also what the consequences will be if he does not meet your expectations.
With the current health emergency and restrictions, he most likely has both some pent-up stress and some pent-up energy. Make sure each and every day that he is getting a physical release by doing something outside in your yard, doing a chore in which he has to move around, lifting weights (which can be with anything that weighs five pounds or more in your home), going on a family walk or even running the stairs for five minutes.
In addition, make sure you allow for some alone time for all the children in the house to separate them a bit. Right now, we are all experiencing a lot of togetherness, so perhaps everyone having some time alone would be helpful. You also might have to clearly identify respect. For him, it might include things like looking at you when you're talking to him; following your instruction the first time, not the second, third or fourth time; listening to you without interrupting; and, for the time, not playing jokes on or having debates with siblings that include any physical touching at all.
You must give consequences once you put these clear expectations into play. These consequences have to be something that motivates your son, and they have to be delivered calmly and consistently. Otherwise, they won't work. In fact, if you follow through nine times, and you let it slide the tenth time because he has been doing so well, he will push it again, thinking, “Maybe this will be the time Mom gives in again." So think about what he likes: Having a cell phone, walking down to a friend's house, sweet snacks, late night TV, sleeping in a bit or riding a scooter? Once you've identified what he likes, take away that privilege when he displays negative behavior. Then make sure he understands that the only way he can regain access to that privilege is by displaying good behavior.
Another strategy would be to reward his good behavior. You don't have to use anything fancy; it could be something like giving him positive praise, making his favorite cookies or letting him stay up 30 minutes later on a given night. Make sure you tell him why he is getting these things. For example, you could say: “Thank you for calming down when you were angry and not hitting your brother."
Another idea would be to add something he does not like when he displays negative behaviors. For example, he has to get up 30 minutes early to complete a chore for a sibling he hit, or he has to accompany you around the house so you can monitor him. Or maybe he has to do something nice for a brother or sister he hurt before he can come out of his room.
We hope this gives you a few ideas to consider. It is time for actions since he is no longer respecting your words.