Good morning @formydad . I had typed a long answer for you and it disappeared! So, I’ll try again.
Your best bet is to go to the American Cancer Society website. There is lots of information on side effects and how to manage them. They might also have support groups for families, which would be great. You’ll also meet other people who are going thru the same thing
The neulasta injection is to support the white blood cells and to encourage growth. Chemotherapy is very hard on WBCs and as their numbers go down, the chance of infection goes up. The doctors keep a close eye on this. They use the term ANC-absolute neutrophil count. Neutrophils are immature white cells. The numbers will drop but the doctor will keep you informed.
Also, now is a good time to find a day planner that has large size monthly calendars and pages for taking notes. Your mom will take it to all appointments and write down everything: next appointments, medication changes, questions she or your dad have, answers, side effects, problems, etc. I was an oncology nurse until I retired and the patients found this very helpful. I hope it will work for you. Take care and think positive! Will you let us know how things go for you and your parents?