I know how you feel. I lost my both sets of grandparents within 18 months. I'm a Christian and I too was also very angry at God. But let me tell you I love him more now for showing my grandparents mercy. Please read on....
my grandmother was diagnosed with dementia, she fought for seven years before the lord decided to take her. This crippled my grandfather. He was so depressed he confided in my father that he wanted to kill himself. A few months later my grandfather was diagnose with stomach cancer he had only a short time to live. He had nothing to live for as his wife had gone. Shortly after the diagnosis he was took into hospital were he died peacefully. My grandfather couldn't live on without my grandmother and he did not want to commit suicide as he was at Dunkirk and saw many a friend slain on the beaches. So he valued life and didn't believe in suicide. He was not in pain with the cancer and it was in the latter stages. God showed mercy by taking him home and no longer being without his wife.
My mothers parents died within two days of each other. My mothers father went into hospital for a heart bypass and came out of the operation fine. The operation was a textbook case. Unfortunately, whilst asleep. the wire holding his rib cage together after the heart operation, came loose and pierced the sack around his heart. The sack filled with blood and crushed his heart. Killing him whilst he slept. My gran was also in hospital recovering from pneumonia and was almost fully recovered. When my family broke the news she relapsed and died within two days saying " What am I going to do without him ? "
What I'm trying to say is at the time we lose a friend or family member we always blame God. We don't know what plans he has for us. We simply have to trust him.