Adiyen does not know Sanskrit, but adiyen recites Desika slokas, Paduka Sahasram and Sahasranama every day. As adiyen does not know its correct pronunciation and as adiyen is over sixty years in age, memorization becomes difficult. Is there atonement for mispronunciation as adiyen wants to recite many slokas?

It is better to recite without mistakes; there is no harm in making minor mistakes, but one must try and rectify those mistakes as well. That is the difference between reciting a Veda and stotras, it is considered erroneous when a Veda swara or an akshara is mispronounced, unlike stotras.
The sloka at the end of Sahasranama appeals to Perumal to forgive our mistakes.
yata3kṣara pata3p4raṣṭam mātrahīṉam tu yat3pa4vet
tat carvam kṣamyatām te3vā nārāyaṇa namostute
Though not all slokas contain such verse. However, when we recite them with devotion, Perumal accepts our flawed recitation like how the elders accept a child’s blabber; but we should strive on our part to recite them without errors.