Must I repeat my Maghrib and Isha prayers due to the obligation of sequence, if I decide to repeat the prayer of Asr, which is doubtful, after the Isha prayer? And is my ablution valid with the presence of qashaf on the eye, and what is meant by dead qashaf that does not fall off?

Doubt about an act of worship after completing it does not affect its validity. Therefore, you should not repeat prayers merely due to these doubts, especially given the presence of waswasah (obsessive whispering). Scholars have differed regarding the order between performed and make-up prayers. The Shafi'is did not deem it obligatory, while many scholars considered it obligatory in all cases. The Hanbalis held that it is waived if there is a fear of missing the current prayer. There is no harm for you in acting upon the Shafi'i madhhab. So, if you owe a make-up prayer, you perform it alone without being obligated to pray what follows it.