Is a husband sinful if he advises his newlywed friends on matters of their private relationship? And what are the limits of such advice?

If a husband's consultations with his friends do not involve disclosing secrets or details about private marital life, and are within the bounds of modesty, free from vulgar language, there is no sin in them. In fact, he may be rewarded for them if his intention is to help his friends fulfill their wives' rights and ensure their chastity. The limits of advice in these matters are evident in everything that achieves a legitimate benefit, repels a harm, or encourages noble morals. Anything other than that must be refrained from, because the original principle is to conceal private matters and not delve into them except out of need or necessity.