Brother in law and sister in law observing strict purdah

Q: I recently heard someone say that it is permissible for the sister-in-law to not make parda from her brother-in-law when: 

1. There is no scope of fitna. 

2. When it becomes difficult for her to leave her own room for basic needs. 

My friend has recently married into a family of 6. They live in a small flat. Her brother-in- law is 6 years younger than her and she claims he is an actual replica of her brother in her maternal home. There isn't a chance that they can ever be alone. It becomes difficult for her to constantly be in her cloak, burkha and pardah the entire day almost as if she is at a guests home and not in a home that she has a right to stay in. What is the ruling regarding this?

Making dua after Eid Salaah

Q: Is it permissible to make dua after the eid salah before the khutbah, thus delaying the khutbah and not making dua at all in the second khutba? 

Did Nabi Sallallahu Alaihi wa Sallam, the Sahaabah. or any of the four Imams or the fuqaha of their madhabs mention making the dua between the salah and khutbah?

Joining salaahs when travelling

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

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 Isha together? Is this permissible and if not, does one get a sin when they do it?