Cape Verde, a former Portuguese colony, is a popular holiday destination due to its golden beaches and year-round warm weather.
Since 2022, Tui has taken more than one million holidaymakers to Cape Verde.
Lawyers say they have been gathering evidence of issues at some hotels in the country. Footage seen by the BBC shows what appears to be undercooked food, buffets surrounded by flies and mould in rooms.
Previously the lawyers said six Britons had died after holidays in Cape Verde since January 2023 but they now believe eight people have died.
Elena Walsh and her family, from Birmingham, were among those who booked a package holiday to the island through Tui last year.
The 64-year-old had been staying at the five-star RIU Cabo Verde resort when she started to feel unwell on 8 August last year. Walsh was taken to hospital, where she died on 10 August.
Her son, Sean Walsh, said his mother had become ill very quickly.
“Through the night, we were there with her trying to see if she’d pull out of it, but she just deteriorated,” he told BBC Breakfast.
He added: “I just want people to not go there. Because, yes people can go on holidays there and come back and be fine but my mum didn’t.
“If people are willing to run that risk, then go for it but I’d say to people: don’t.”
RIU Hotels and Resorts said the health and safety of guests were its main priority, adding: “Our hotels in Cape Verde follow the strictest international health and hygiene standards, certified by external prestigious consultancy firms, specialised in health and safety.”