Is it permissible to perform tayammum for prayer if warm water is unavailable for ghusl from janabah for those residing abroad, and should tayammum be repeated for each prayer or is it sufficient once?

You must perform a ritual bath (ghusl) to cleanse from janabah as long as you are able to, even if by heating water and bathing in a warm place. If you are unable to perform ghusl due to illness or fear of worsening an illness, then you are permitted to perform tayammum (dry ablution). If you are able to wash some parts of your body, then wash them and perform tayammum for the rest. If you are completely unable to wash your entire body, then tayammum will suffice. Wudu (minor ablution) is not sufficient for janabah, and you must perform tayammum for each prayer as long as you are unable to perform ghusl. You must also make up the missed prayers immediately and repent from masturbation.