How can I stop thinking about death? What should I do to stop fearing death?

Hello and thanks for reaching out! It sounds like thoughts about your family members passing away happen daily and are really painful to think about.  It must be difficult to be located in another country and physically so far away from them, even if you don't normally see them a lot. You mentioned your Mom has lung disease and you worry about her frequently and I think that's understandable.  It's scary to have a loved one who has medical issues.  There's that lack of certainty if the treatment(s) will work or not and concerns about their level of comfort.  And then of course, worst case scenario dealing with someone passing and whether you are ready to deal with that pain. While you won't be able to prevent your Mom from eventually passing (we all pass eventually as part of the life cycle), you can make sure you spend time with her (on the phone, in person) and share how much you love her and some of your happy memories together.  Try to remind yourself to stay in the present moment, in the here and now.  Today, she is alive and on this earth so make use of your time together.

As for your brother who struggles with a substance use disorder (alcohol), it sounds like you worry about him taking care of himself and/or making safe or unsafe choices. I'm going to assume he's an adult and capable of taking care of himself physically, if he chooses.  If that is correct, sometimes the best thing we can do for ourselves and our loved one(s) is to remind ourselves that we can't control other people or their behaviors.  The only thing we can control is ourself/our responses.  Try to do something to take care of yourself (physically, mentally, spiritually) while educating yourself more about substance use disorders.  You can control how much time you spend with your brother, you can control making calls to him and/or visiting him, and expressing how you feel (if you feel comfortable with that), but he has to be willing to make different choices for himself to prevent health issues or other consequences from alcoholism. 

Panic attacks can be scary and super disruptive.  I'm sorry you have to experience those.  They aren't fun!  Distraction can be helpful (focusing on things around you/outside yourself), as well as different forms of mindfulness, using positive self-talk to remind yourself that in this moment you are safe and these feelings are just feelings and will pass, progressive muscle relaxation, etc. Have you taken time to track what happens before a panic attack? What feelings or thoughts or situations are happening before you experience a panic attack? 

Here's a link to a no-cost community resource available here in the U.S. - Adult Children of Alcoholics and other dysfunctional families (ACA).  You can visit the website and look for online, phone, or in-person meetings in your area.  I think you'd benefit from the information and support. WWW.ADULTCHILDREN.ORG

I wish I could help you resolve the distressing feelings/worries and panic attacks with just one written message, but I don't have a magic wand.  I'm happy to support you with working through these feelings and developing skills to manage if you'd like to connect.  Either way, take good care!