Thank you for contacting Just Answer.
I am sorry to hear about the problems you are experiencing with your son. It is understandable that he may be acting out due to the recent changes in the family that he may be having difficulty adjusting to. It is difficult to determine whether these behaviors are suggestive of a psychological problem, or if they are merely reactions to the stressors in the family. One way to tell is this. Keep in mind that any behavior that gets attention is likely to continue happening. It has been called the law of the soggy potato chip in that if a child thinks that he has a choice between a soggy potato chip or no chip at all, he will choose the soggy chip. If your son feels, for whatever reason, that he has the choice between negative attention from or no attention at all, he will choose the negative attention and so he will act out until he gets it. The only way for this pattern to stop is for you to begin to catch the good behaviors and reward them with attention, and to calmly and matter of factly give consequences for the negative behaviors with as little attention as possible. A very good book on this subject is Win the Whining War & Other Skirmishes: A Family Peace Plan by Cynthia Whitham MSW. The more consistent you can be with this positive parenting, the more secure your son will begin to feel and the more his behavior is likely to improve. If on the other hand, after consistently employing this technique you see no improvement, I would recommend an evaluation by a child psychologist to rule out any other issues.
You may try reading books with him about teasing that will model how to cope with teasing in a healthy way.
I hope this answer is helpful. Please let me know if I can clarify further.