Jolly has confessed to all the six deaths between 2002 and 2016 in her family and on Monday for the first time, all the three were seated together and questioned.
The police probe team is divided into six separate units besides a technical team comprising of forensic, legal and police experts.
Jolly's second husband Shaju and his father Zachariah were summoned by the police on Monday mornung and were first questioned individually and then jointly. Later, Jolly was also brought in.
Meanwhile, one of the arrested M. S. Mathew, who procured cyanide for Jolly from a jewellery worker Preju Kumar (also arrested), confessed to the police that he paid Rs 5000 and two bottles of liquor to him.
A woman revenue official, Jayashree, who helped Jolly in her real estate dealings, was questioned by her superior officers.
Technical team head Divya Gopinath, an IPS officer, said that the probe is going on well and the autopsy report of one death (Jolly's husband - Roy Thomas) is available which talks about the presence of cyanide but it has to be proved scientifically.
"A number of tests have to be done and we are confident of proving it, but we know it's not that easy also. We are on the lookout for more evidence," said Gopinath.
On Monday morning, the complainant - Jolly's first husband's brother, Rojo Thomas landed at Kochi airport from the United States and police gave him security till he reached his sister's home near Kochi.
On Tuesday, he is likely to present himself before the probe team led by Superintendent of Police K. G. Simon.
The first to die an unnatural death in 2002 was Jolly's mother-in-law Annamma, a retired teacher. She was followed by Jolly's father-in-law, Tom Thomas, in 2008. In 2011, their son and Jolly's husband, Roy Thomas, died. It was followed by the death of Roy's maternal uncle, Mathew, in 2014.
The two-year-old child of Sily (Shaju's first wife) died the following year, while Sily passed away in 2016.
( With inputs from IANS )