Peter Cairns, 26, was knifed in the heart in parkland at Rough Park Way, Telford, on July 11, 2021.
During a lengthy trial at Stafford Crown Court, jurors were told that the incident involved four weapons; a knife, a blunt Samurai sword, a wheel-brace and a hammer.
A third teenager, now aged 16, was cleared of both murder and manslaughter, and was released from custody while a fourth had already pleaded guilty to Mr Cairns' murder.
The 11-strong jury decided the two guilty verdicts unanimously following 17 hours and 46 minutes of deliberation.
Speaking immediately after the result was announced Peter's mum Lisa Cairns, aged 50, and his brother Adam said her family "miss Peter every day" but she was "happy with the outcome" decided by the jury.
"I would like to thank everyone who has supported and shown love towards our family and Peter."
The three defendants were also charged with an assault occasioning actual bodily harm on Mr Cairns’ friend Kaine Bushell. The same two defendants were found guilty of that, with the third young man found not guilty.
Thee two convicted teenagers, as well as the one who admitted killing Mr Cairns, will be sentenced in July.