Im scared for the days my dogs pass away.?

It sounds silly, i know. But i love them to death... theyre family. Ive had them both since i was little. Im 15 now and one dog is 8 , the other is 7. I recently found out that one has a brain tumor, and days after i found this out my other dog was diagnosed with diabetes. Both of them have terrible issues all at the same time and im scared im going to lose them sooner than i expected. Im so scared and i dont know how to handle losing a pet. Only pet ive lost was a gerbil but thats obviously not near having a dog pass away. Theyre my family! They arent dying right now but im scared for when the time comes.