Deep conditioning is a great way to soften up your hair. Get Greek yogurt and put in castor, olive, and coconut oil along with a rinse out conditioner.
Put it in your husband's hair and leave him under a hooded dryer for 30-60 mins. If you don't have a hooded dryer then a shower cap on his head then a plastic bag over the shower cap. Use a blow dryer between the plastic bag because it will heat up the hair cuticles keeping them moisturized and soft.