Militch, described as the "most culpable", showed little remorse, and was given a term of eight years and four months with a minimum non-parole period of five years.
Zimmerman was sentenced to seven years and must at least serve three years and six months. Windley was given five years with a minimum period of two and a half years.
After the sentencing, Valentine's step father John Timmer-Arends said he was stunned.
"As far as I'm concerned it's not enough...but given what the judge can do within the law I think it's reasonable."
He and his family had been through "17 months of hell" and no amount of time would change that.
"Even though the sentencing is now over, nothing changes for us."
Thirteen victim impact statements were provided but only four were read in court including one from Valentine's mother, Lynda.
"This is the last thing I can do for Michael...no one can understand the pain until you've had a family member [killed]. Nothing could prepare you for something so cruel."
She described the "terror" of lying awake every night reliving her son's last moments, and the pain she feels watching her grandson grow up without his father.
"This is a life sentence for us...I will never forgive them. I wish they were dead and not my beloved Michael."
Laura Hill, the mother of Mr Valentine's four-year-old son Luca, told the court her little boy had become overwhelmed with sadness, struggling with emotional problems both at home and at school.
"He is painfully aware...I asked how he felt on that day and he said to me, 'I have a headache and there is a pain in my heart that won't go away'."
All three men previously pleaded guilty to one charge of perverting the course of justice and were given a sentence of 12 months to serve concurrently.
