I have 8 brothers and sisters. I am the baby. All of my siblings were athletic and very thin as kids and for some into their early twenties. As was I. The people in my family who eat well and exercise (myself, my two marathon running brothers, my sister who has MS) are all not only thin but look 20 years younger than our age with fabulous bodies and skin to march. The rest are obese, gray, and just plain old and look their age and older.
The only difference is our lifestyles. Period.
By the way. I am small framed and 5'6. One of my sisters that is monstrously obese is also small framed and 5'6. If you put us two together I look like a 20 year old super model and she looks like something out of joba the hut.
I love her but girlfriend just kept eating crappy foods and not exercising.
All those siblings will die way before their time.
While you have a point it does not explain it all.
My family is very athletic, marathoners and all that.
Pop died young from a heart attack.
His Identical twin, also a marathoner lived 15 years longer and died of respiratory problems.
They had virtually identical genes and lead the same lifestyle.
I smoke and drink, I might drop tomorrow or at 90.
Who knows?
Here is where you are misguided. It is true those overweight fat siblings of yours have the ability to lose weight and get back into shape. The can eat normally and with moderate exercise achieve that goal.
The genetic endomorphs cannot do that unless they train like Olympic athletes and eat like Bergen-Belsen inmates FOR THE REST OF THEIR LIVES.