First of all, please note that when men sleep, the Testosterone increases in their body so that's not abnormal to see them in that way while sleeping. However, we must also not forget the rule of Satan in the dreams. So below are some tips he can practice:
The dream is the child of the past day. usually we dream about what we think. We must be careful of our thoughts and fantasies before going to sleep, because if we cultivate any thoughts and fantasies in our minds before going to sleep, we will see them in our dreams. In fact, our ideas, desires and inclinations are expressed in dreams. The solution is that:
During the day, we should be careful not to allow wrong thoughts to enter our minds.
Avoid reading, listening and thinking about sex, as continuing to do so has dangerous consequences, causing trouble for us in both sleep and wakefulness and depriving us of relaxation.
Try to sleep with Wudhu (Sahih form of Wudhu: https://youtu.be/snH7kSjgLuw)and recite the Qur'an a little before going to bed.
If you can, wake up after the morning call to prayer and before sunrise.
Try to control your imagination before going to bed and do not think about arousal and sexual issues.
Always have things to think about when you are unemployed or at bedtime so that you do not have the opportunity for sexual fantasies.
When sleeping, do not sleep on your stomach. Exercise regularly and a lot in order to drain the body of excess energy.
One or two days a week, the recommended fast is useful, and if you can not afford it, reduce the amount of food consumed and increase the interval between meals, or reduce the number of meals and be satisfied with the minimum amount of food.
Avoid talking softly, jokingly and laughing with strangers.
Before going to bed, recite this Dua mentioned in the authentic book Mafatih to prevent the wet dreams.
اللهّمَ اِنّي اَعُوذُ بكَ منَ الأحتلام و مِن سُوءِ الأحلامِ و مِنْ اَنْ يَتلاعَبَ بِيَ الشيطانُ في اليقَظَةِ و اَلمنامِ
The above tips were general solutions which means works even for single people, but as your husband is married and he still has wet dreams, that may indicate that