Jay Stewart, 18, Cole Turley, 18, and a 15-year-old boy who cannot be named for legal reasons were found to have acted together to carry out the attack at Irvine beach in May last year.
Kayden Moy was fatally stabbed on the picturesque beach on May 17.
Appearing at the High Court in Glasgow on Tuesday, Turley admitted to the killing, while Stewart and the 15-year-old were found guilty of murder last month following a trial at the High Court in Glasgow.
All three had been members of the Murray Boys group, while Kayden and others were part of the Himshie group in East Kilbride.
In a message on social media posted ahead of the sentencing, Kayden’s father Paul Moy said: “Nothing that happens in that courtroom will ever bring our son back.
“No sentence can fill the emptiness, the heartbreak, or the lifetime of memories we’ve been robbed of.
“Tomorrow is not about closure, because there is no such thing when you lose a child.
“It is about justice, accountability, and making sure my son’s life is remembered.
“Forever loved. Forever missed. Forever my son.”
During the trial the jury heard that shortly before the attack Turley, Stewart, and the 15-year-old had been at the top of a sand dune throwing rocks at people on the beach.
Kayden’s girlfriend Keryn Knox, who had been with him at the beach, said they had been getting ready to leave at about 6pm when the rocks started to be thrown, and Kayden had gone up to confront the teenagers.
Ms Knox told the court: “I went up with him to try and stop him. At that point he had run up the hill and he was just shouting stuff back.
“Then Cole ran in from the side and Kayden has seen a blade and when he tried to run he slipped, and when he tried to get back up Cole has stabbed him in his left lower side twice.”
Ms Knox told the court: “His body turned completely white and his limbs were blue and people were crowding round him, trying to put his T-shirt over the wound.”
Another witness said he had gone with Kayden to confront the teenagers, and that as they reached the top of the dune, Turley brought out a knife and Stewart an extendable baton.
The witness said: “Then out of nowhere Cole (Turley) just started running at us. I ran to the right, so did Kayden, I jumped over a grass ledge, Kayden slipped and Cole leaped over and jumped on him.
“He had a knife and it hit. I saw one stab.”
The 16-year-old was so badly injured in the attack that he later died.
Stewart and the 15-year-old had denied the murder charge and had lodged special defences of incrimination.
However this was rejected by the jury, who found both guilty of Kayden’s murder after a trial lasting more than two weeks.

World Affairs Correspondent