The victims, including local health officials and journalists, went missing after their delegation came under attack from angry locals during an outreach visit to the southern town of Womey in September last year.
Eight bodies were recovered from the septic tank of a nearby primary school two days after the attack.
"We argued for two days, but we didn't make ourselves heard and Judge Mohamed Diop issued a heavy penalty that we are going to challenge at the supreme court," defence lawyer Michel Labile Sonomou told AFP.
Prosecutor Williams Fernandez said he was "very satisfied with the decisions that have been taken" at the sentencing late on Tuesday.
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"As a prosecutor, I always ask for the maximum to get what I was aiming for, because I know that Guinea does not carry out death sentences, although it is still provided for in our penal code. So it's a good decision," he told AFP.
The deadliest Ebola epidemic on record has killed nearly 11,000 people in west Africa, according to the World Health Organisation.
Many Guineans believed local and foreign healthcare workers were part of a conspiracy to deliberately introduce the outbreak, or invented it as a means of luring Africans to clinics to harvest their blood and organs.
A police lieutenant told AFP the Womey outreach team was targeted by protesters who had come "to kill them because they think Ebola is nothing more than an invention of white people to kill black people".