Encourage your wives to wash away any traces of feces and urine from themselves, as we feel shy in their presence. Indeed, the Messenger of Allah ﷺ used to do that.
مُرْنَ أَزْوَاجَكُنَّ أَنْ يَغْسِلُوا عَنْهُمْ أَثَرَ الْغَائِطِ وَالْبَوْلِ فَإِنَّا نَسْتَحِي مِنْهُمْ فَإِنَّ رَسُولَ اللهِ ﷺ كَانَ يَفْعَلُ ذَلِكَ