Do you think is due to their lifestyle? eg. too much stress.. too much processed food in their diet.. or too much sugar?

If it's in the family there's nothing they can do. My paternal aunties & uncle all died from heart attack.
Kinda unfortunate your aunty had to cook in an enclosed kitchen. How could she have stood the smoke & oil is beyond me.

Tis is what Ai replies when i queried about breast cancer & pregnancy

Here's what research shows about the relationship between pregnancy and breast cancer:

Long-term protective effect: Having a full-term pregnancy, especially before age 30, actually reduces a woman's lifetime risk of breast cancer.
Temporary risk increase: There is a short-term increase in breast cancer risk following pregnancy, which typically lasts for about 10 years. This may be due to hormonal changes that can stimulate the growth of existing cancer cells.
Multiple pregnancies: Women who have had multiple full-term pregnancies generally have a lower risk of breast cancer than women who have never given birth.
Breastfeeding: Breastfeeding for a total of one year or more (combined across all pregnancies) further reduces breast cancer risk.
Age at first pregnancy: Women who have their first full-term pregnancy at a younger age (before 30) have a lower risk of breast cancer compared to women who have their first child later in life or who never have children.