Your sister is at the top of the stress scale: New marriage, a move, a job she isn’t happy with, husband in medical school, apart from her support system and now quarreling with the husband. No wonder she is having panic attacks. She is reacting to what for her is an overwhelming situation.
This is complicated. Since I don’t know the whole story, I may be only repeating what you and the rest of the family already know. As a married woman, her husband is the one who should be at the forefront. I’m concerned that one of the things the couple is fighting about may be your family’s involvement.
I do understand why you and your parents are so concerned. But this couple has to start working as a team during this difficult time or the marriage isn’t going to make it. They both need encouragement and support.
I think your best bet is to sympathize with her and her husband. Let them know that you understand why they’re having such a tough time managing their situation. Make sure they know that you are all on the side of the marriage. Suggest they get into couples counseling to help them figure out how to manage the multiple stresses they are under. Then cut back on the advice and give them lots of love. If you can give them a vote of confidence, they may rise to the occasion.
I wish everyone well during this challenging time.