A Polish couple and their seven children, killed by Nazis during World War II for hiding Jews, will be beatified Sunday, the first time an entire family is given one of Catholicism's highest honors.

The ceremony in the family's hometown of Markowa in south-east Poland will be attended by over 30,000 people, including 80 bishops, 1,000 priests, the country's chief rabbi, and an Israeli delegation.

It was there, on 24 March 1944, that German police acting on a tip-off shot dead Jozef Ulma and his wife Wiktoria, who was seven months pregnant and partially gave birth during the execution.

Their children, Stanislawa, Barbara, Wladyslav, Franciszek, Antoni, and Maria, aged between two and eight, were killed too, along with the eight Jews the family had been hiding in the attic.

The eight — Shaul Goldmann and his five children, including his daughter Lea Didner and her five-year-old daughter, and Golda Gruenfeld — were also shot before the family farmhouse was looted and set on fire.

The police fired up into the attic from the floor below, "and the blood of the victims began to drip from the ceiling… onto a photograph of two Jewish women lying on a table below", Vatican News said.

That photograph "has been preserved as a 'relic'", it said.

Baptism of blood

The massacre followed "a story of love and friendship", said Italian journalist Manuela Tulli, who has written a book on the family along with Polish historian and priest Pawel Rytel-Andrianik.

"When the Jews asked for help, they opened their doors. They lived together for a year and a half, cooking and eating together", Tulli told AFP.

Jozef Ulma was a keen photographer as well as a farmer, and photographs he took that survived reveal the family's life through simple, everyday scenes.

"We see the children running barefoot in the grass, doing their homework, the mother hanging out the washing," Tulli said.

The families were denounced by a Polish policeman. After they were executed, 24 Jews in Markowa were murdered by their Polish neighbors.

The Ulma family will be the first ever to be beatified, a key step on a possible path to sainthood in the Catholic Church.

And in a rare move, the Ulmas' newborn seventh child will also earn the title of "blessed".

The child is eligible for beatification through the concept of "baptism of blood", having been born "at the time of the mother's martyrdom", according to the Vatican's department for saints.

Usually, people need to have performed a miracle to be eligible for beatification, but martyrs are exempt.

Jozef and Wiktoria Ulma were recognized by Israel in 1995 as members of the "Righteous among the Nations", an honor for non-Jews who tried to save Jews from Nazi extermination.

The family also has a museum dedicated to it in Markowa and in 2018 Poland decreed 24 March — the date of the massacre — a day of remembrance for Poles who rescued Jews during the German occupation.