I understand colonoscopies are recommended starting at age 50. My father was diagnosed with rectal cancer at 45 years of age, does that change the recommendations of when my brother and I should be checked?

Yes, it will change the recommendation. If you have a first degree relative (a parent, sibling or child) diagnosed with colon cancer prior to the age of 60, you need to start your colonoscopy screenings at age 40 or 10 years prior to the age of diagnosis of your relative with colon cancer (whichever is younger). So for you and your brother the recommendation would be to start colonoscopies at 35 years of age.