Is it permissible for an epileptic patient who is unable to stand to perform tayammum and pray when he is in a state of janabah? And how should tayammum be performed for one in a state of janabah? And is it obligatory to repeat the prayer that was performed with tayammum if he later becomes able to stand and perform ghusl?

Whoever is afflicted with an illness must fulfill their obligations to the best of their ability. So, whoever is able to perform ghusl sitting down should not suffice with tayammum. Tayammum for janabah is like tayammum for wudu, and its description is wiping the face and the palms of the hands. The prayer of a sick person performed with tayammum is valid, and they are not required to repeat it upon recovery; rather, they should perform ghusl for future prayers.