Answer to Q1. I think the musketeers are deeply trusted men chosen because they are loyal to the king and good at handling swords and muskets. There must have been a lot of people against the king, so there must have been many dangers for the king. With only the guards, it still lacks protection. So, he chose musketeers for something a bit like personal bodyguards.

Answer to Q2. People are usually gentle to people that are gentle to them and fierce to those who are fierce to them. The musketeers, more than others, must have this tendency. So, my guess is that Treville must have treated his musketeers very well. He must have encouraged and was gentle to them.

A1. Musketeers is someone who are very good at swordfighting or just fighting, and they work for the king, Louis the thirteenth. In those days, Louis the thirteenth didn't have the greatest strength so he made a group called musketeers who will be royal to be and will protected him and will do whatever he wants them to do. So musketeers are like Louis the thirteenth's personal bodyguard, may I say? haha.  Because even though they are very hot-tempered, they always fights for the king and even tries to risk their own life, so I think that the musketeers are very similar to the bodyguards.

A2. I think that Treville must have shown many kindness and forgiveness, compliment toward them. Juding by the fact that all of the musketeers shows many mercy and kind hearted appearence to the people who are poor, I'm guessing that the Treville have shown kindness to them, so they can show kindness to the other people. Or maybe Treville will judge whoever who wants to be a musketeer and depends that the person is whether or whether not a brave or gentle person. But anyone who wants to be a musketeer will have a great courage, I think. Because as I told you in the Answer 1, Louis the thirteenth wasn't have the greatest power in the country, and the musketeers are for him, then it will be pretty dangerous to be a musketeer. So possibly, even if Treville didn't behaved to them nicely, they would have all great royalty to Treville and the king, I think.

1. Louis the thirteenth was always exposed to danger expecially from the guards of the cardinal. The musketeers were supposed to protect the Queen and Kings safety and also fight for him against his enemies. Musketeers who have great faith such as Athos, Porthos and Aramis sometimes get secret missions from the king.

2. Musketeers are brave against there enemies and warm hearted to weak people. Trevile would have shown leadersip to them by working himself for hard people and fighting against kings enemies bravely. From these aspects of Trevile the musketeers would have faith on him and think him as the true leader of the musketeers.