I'm sorry to hear about your loss.
My dad passed away when I was 16. He had a heart attack, recovered, but then went into cardiac arrest during a routine angiogram. He needed a heart transplant but the machines keeping him alive caused some of his other organs to fail and there was just nothing they could do to save it all.
The first few months were pretty surreal. I remember just sitting, thinking, slightly detached from everyone and everything, wondering how it was possible for the world to go on as though nothing had happened when I had just lost one of the most important things in my life.
Lean on your family and let them lean on you. Looking back to the time shortly before my dad died and shortly after, everyone sort of pushed back their own pain at moments to comfort each other. I remember times when my mom put on a brave face for me because I was so devastated, and seeing that she could be okay made me feel better. There were other times I put on a brave face for her because she couldn't anymore, and I realized that I could be okay, too, even if I was just pretending.
Remind yourself that it's okay to cry. It's okay to laugh and be happy, too. I remember laughing pretty hard about something a couple of days after he died and feeling guilty. Let whatever happiness you can find in. Let in the sadness, the grief, the anger, everything. Trying to ignore it or forcing yourself to feel a different way will just prolong the process.
I always found writing to be a wonderful outlet. I would write about why I loved him, why I miss him, and why I will always miss him. I wrote about the experience of watching him die, right down to the gory details. Literally everything that came to my mind regarding my dad, I wrote down when I had the chance. It was sort of my way of talking about it.
My mom joined some sort of support group online for other people who had lost their spouses. I know it helped her immensely. I'm not sure if that's something your mom would be interested in - mine definitely wasn't the "online friends" type of person before but I know she found a great deal of comfort speaking to people who had experienced the same loss.
Know that eventually things will feel normal, because they have to. It will be a different normal, but you'll learn it. For now, focus on grieving and take things day by day.
I hope you and your family can find some peace in this very difficult time.