Is it permissible to wipe over part of the face and forehead if the niqab covers them and it is difficult to remove it for every prayer, bearing in mind that ablution is performed before wearing the niqab, and is it obligatory to make up for the missed prayers that were performed in this manner?

Wiping over a niqab that covers the face is not sufficient; rather, washing the face during ablution is obligatory according to the consensus of scholars. As for wiping over a khimar that covers the head, it is permissible according to many scholars if it was worn in a state of purity. If you prayed having wiped over a part of your head from above the covering, there is a difference of opinion regarding the obligation of repeating the prayer, but repeating it is more cautious.