By Rory Smith and Anna Cardovillis, CNN

(CNN) -- Few people share as much in life as conjoined twins. For Maria and Consolata Mwakikuti, conjoined twins and orphans from Tanzania, this was certainly the case.

But at 2:30 p.m. local time on Saturday, Maria passed away. Fifteen minutes later, so, too, did Consolata.

The twins were conjoined at their abdomen and shared organs such as the stomach and part of the aorta, a crucial artery that runs from the heart down to the abdomen. They had separate heads and hearts.

Early investigations soon after their birth confirmed the two sisters could not be separated, said Dr. Faith Kundy, a physician at Iringa Regional Hospital, where the women died.

In December, Maria was diagnosed with a respiratory problem resulting from an inoperable chest deformity, the ultimate cause of her death, Kundy told CNN.

"They underwent tests and it was very unfortunate that nothing could be done," said Kundy, who was with the twins during their last few days. "It was very sad for me. Apart from being patients they were friends, they were funny people. I feel so sad because they had a hope of living."

But Kundy added it was a major achievement that the twins reached age 21.

Maria and Consolata were taken care of by a congregation of nuns, the Consolata Sisters, and were born at the Consolata Regional Hospital, where their parents left them after birth, according to Sister Jane Lugi.

"They were very lovely, very enthusiastic," Lugi said. "Their plan was to work and to help other people less fortunate in the community. They were suffering of course but they were able to live and want to live. In spite of the bonding condition, they had passion for life."

The women had been studying education at Ruaha Catholic University, added Kundy.

Having become well-known in the East African country, and an inspiration to those who knew them, the twins' deaths cast a somber spell on the country on Sunday.

"I'm saddened by the death of Maria and Consolata. When I visited them at the hospital, they prayed for the nation. Their dream was to serve our nation. Condolences to their family ... and all those affected by their deaths. May they rest in peace," tweeted Tanzanian president John Magufuli in Swahili.

Living with a disability is notoriously difficult in Tanzania. People with disabilities make up some of the poorest and most marginalized segments of Tanzanian society, according to Comprehensive Community Based Rehabilitation in Tanzania, an organization that provides rehabilitation and disability services across the country.

More than half of children with disabilities don't attend school. Illiteracy among people with disabilities is 46% compared to 25% for people without a disability.

Maria and Consolata not only went to school, they vowed to become teachers.

"Rest in peace Maria and Consolata -- you lived your life right when you were here on earth," tweeted Tanzania's Deputy Minister for Health Faustine Ndugulile.

Conjoined twins are extremely rare, with an incidence of 1 in 50,000 births, according to a 2017 paper in the journal of Clinical Anatomy. However, because around 60% of those cases are stillborn, the actual incidence rate is closer to 1 in 200,000 births, according to the study. Almost 70% of these twins are female.

The most famous case of conjoined twins is that of Chang and Eng Bunker of Siam, now Thailand. The brothers, who lived for 63 years, and ended up having a total of 22 children between them, popularized the term "Siamese twins," according to the study.

Scientists believe that conjoined twins result from a single fertilized egg that fails to separate completely. However, the scientific community remains divided on why this happens.

Separating twins is a complicated and dangerous procedure, and not all twins -- because of shared organs or other complications -- can be separated.

Despite remaining conjoined, Maria and Consolata lived the life they could.

"For us it was a good challenge to have disabled people who had a passion to live and for people in Tanzania that passion is what remains," Lugi told CNN.