My brother just ped away..?

My brother ped away four months ago. He had a wife of about a year and a new baby boy only six months old - both he loved so much and they loved him too. But my sister-in-law just barely got re-married yesterday. I know that my nephew needs a dad but it still seems so soon. She lives in Arizona and we live in Utah so it's a good twelve hours away. She didn't even send an announcement to us and my mom understands why she did what she did but my dad is extremely resentful to the fact that she got married four months after my brother's death. It's hard to be there for my family when it seems I can hardly hold up with this burden. My family is extremely close so it just makes it more difficult. It's hard to focus on school work (I'm seventeen - a senior) when I'm stressed with family life. What else can I do?