The answer to the question of how many suns can fit into the biggest star is impossible to answer definitively. While the size of the sun is relatively consistent, the size of stars is much more variable, ranging from the smallest red dwarf stars which are only a few times larger than Jupiter to the largest supergiant stars which can be thousands of times larger than the sun.
The most massive star in our galaxy is VY Canis Majoris, located in the constellation of Canis Major. This hypergiant star has an estimated mass of 150-250 times that of the sun and a diameter of around 1,420 times the sun's diameter. This means that VY Canis Majoris is so large that it would take up nearly one-third of the distance from the sun to the nearest star, Alpha Centauri.
Theoretically, the number of suns that could fit inside VY Canis Majoris is impossible to calculate. This is because the star's interior is extremely complex, with layers of hot, dense gas that are constantly changing and interacting with each other. In addition, the density of the star is not uniform throughout its interior, but rather varies from place to place. It is also impossible to know for sure how much of the star's mass is in the form of hydrogen and helium - the two main components of stars - and how much of the star is made up of heavier elements such as carbon, nitrogen, and oxygen.
In addition to its size and mass, the temperature of VY Canis Majoris also affects how many suns could fit inside it. The temperature of the star is estimated to be around 12,000 K, which is much hotter than the sun's 5,778 K. This means that the star's interior is much more energetic and turbulent than the sun's, and the number of suns that could fit inside it would be greatly reduced.
The only way to accurately estimate how many suns could fit inside VY Canis Majoris is by creating a computer model of the star and running simulations to determine its internal structure. This is an incredibly complex task, and one that may never be completed. As a result, the question of how many suns can fit inside the largest star is likely to remain unanswered for the foreseeable future.