Is it permissible to supplicate: "O Allah, give my parents from my good deeds, and give me from their bad deeds"? And what should I do when I make a mistake in the number of prostrations during prayer due to lack of concentration after the death of my parents?

It is permissible to supplicate that Allah grants your father from your good deeds (hasanat). However, it is not permissible to supplicate that Allah burdens you with your father's sins (sayyi’at), as this falls under transgression in supplication. Allah has forbidden injustice upon Himself, and a person cannot be burdened with the sins of another, according to His Almighty saying: {And no bearer of burdens will bear the burden of another}. Instead, one can supplicate for forgiveness for parents and for believers, as the prophets did.

As for doubt in prayer, if it reaches the level of obsessive whispering (waswasah), then do not pay attention to it. If it is an ordinary doubt, then build upon the lesser (number of rak'ahs) and perform the prostration of forgetfulness (sujud as-sahw).