1) We did a minat with my sisters that we will read an entire Quran together. In my mind my niyyat was to read together turn by turn like I read first then she reads. In her mind her niyyat was that we finish the Quran but we read one sipara each of us separately. So I explained her when we start so we followed my niyyat but its really hard that sometimes we miss it Is it possible to change the niyyat and follow hers?
2) And for the days that we missed , do we have to do something in addition to isteghfar?