I say, and with God's success: It is considered that if he does not find someone to perform ablution for him, it is permissible for him to perform tayammum by consensus. If he finds someone to perform ablution for him but that person is not one of his obedient ones, it is permissible for him to perform tayammum. If he finds someone who obeys him, there is a difference of opinion on this matter. The prevailing view is that neither spouse is obliged to perform ablution for the other nor to take care of him in matters related to prayer, and neither is considered capable by the ability of the other. And God knows best.