Ruling on joining two prayers due to attending lectures abroad

He fell asleep and missed prayer in congregation

Joining Zuhr and ‘Asr because of military manoeuvres

He has an exam that will cover the time of ‘Asr and Maghrib – how should he pray?

It is difficult for him to pray qiyaam because of his work situation and because he is a heavy sleeper

Joining Maghrib and ‘Isha’ because of the curfew

What is the ruling on giving two adhans and two iqaamahs when joining prayers?

How should missed prayers be made up?

How should members of military units pray on the front line?