Salaah

Folding one's hands in the last rakaat of the sunnats of fajr while sitting and performing salaah

Q: If sitting down and performing sunnat of Fajr, after the last sajdah of the salah, one puts their hands up again for Surah Fatiha, but remembers before reciting anything, and then goes to continue tashahudd, should a qadha be recited for this salah? And should one have made sajdah sahw in such a case .

Joining salaahs when travelling

Q: Is it permissible to join the salaahs when a person undertakes a journey and is a musaafir? 

For example, you are leaving a country and it is zuhr time, so before the flight, you join zuhr and asr? Or you visited a country and you go to a shop and maghrib time sets in, so you read maghrib and esha together. Is this permissible, and if not, does one get a sin when they do it?