It's a strange thing.
Although Li Yuan's father Li Xun was not the eldest son, he also inherited the title of Duke of Longxi Commandery (龍西郡公) by his father Li Hu (in the Northern Zhou Dynasty, he was renamed Duke of Tang). But after all, it was because Li Xun's eldest brother Li Yanbo stayed in Eastern Wei, and the second brother Li Zhen died early, it was only his turn that it was clear.
1. But what happened to Li Yuan's three brothers?
After Li Yuan became emperor, he posthumously enfeoffed three older brothers, namely Li Cheng the Prince of Liang, Li Zhan the Prince of Shu, and Li Hong the Prince of Han. Because the history books record that Li Yuan's father only had one wife, DuGushi (Dugu Xin's four daughters), does this mean that these three brothers are all brothers of Li Yuan's father and mother?
However, if this is the case, then these four people are all Li Xun's concubines, so in any case, according to the order of the eldest and youngest, it will not be the turn of Li Yuan, who was only 7 years old at the time, can it be said that several of Li Yuan's brothers have already passed away at that time? However, we know that at least the second brother of Li Yuan's three brothers, Li Zhan, has two sons, namely, the eldest son, Li Boyi, and the second son, Li Fengci. Then, in terms of age, the age span between this second brother and Li Yuan at that time should be at least about ten years old.
Moreover, these three brothers must have died before Li Yuan attacked the lord, so that Li Yuan can be regarded as a reasonable heir.
2, however, if this is the case, there are two problems that do not make sense.
1, How old did Li Yuan's three older brothers die one after another, although there were more wars at that time, but three teenage sons died in battle one after another, was Li Xun a little too selfless?
2. If Li Zhan died before Li Yuan attacked the Duke of Tang, then Li Boyi and Li Fengci were born at least before 572 AD. However, Li Boyi was promoted to Shangshu during the reign of Emperor Gaozong, and Li Zhi of Tang Ascended to the throne in 649 AD, that is to say, Emperor Gaozong of Tang was promoted to Shangshu when his uncle was 77 years old, and at the time of Xianqing (656-661), Li Fengci was still the governor of Wonju, and at this time Li Fengci was already 80 miles away. It's not impossible, but it's still a little unreasonable.
3, greater possibility
Dugu Xin's four daughters, Li Yuan's biological mother, are historically unknown, but they should be between 538 and 544 AD, because Du Gu Xin fled from Eastern Wei to Western Wei and arrived in Chang'an in 537 AD, and then had his second son Du Gushan in 538, in addition, Du Gu Xin's seven daughters DuHu Jia Luo was born in 544 AD, so Li Yuan's biological mother was born between 538 and 544, and it is more likely that it was between 540 and 542 AD.
If you count according to the age at which Duhu Jia luo married Yang Jian, the Emperor of Suiwen, that is, 14 years old, Li Yuan's mother married Li Xun between 543 and 545 AD, so it is said that if Li Yuan's other three brothers were all Li Xun's concubines, then their ages should not be more than ten years old.
4, although this possibility exists, but it seems a little unreasonable.
So, there are only two more likely ones:
1. Li Yuan's three older brothers are all Shu out, or at least the second brother Li Zhan is Shu Out.
2. Li Xun or the Fox Orphan Clan abolished the Long Li Young.
Only these two possibilities can explain that Li Zhan was still alive after Li Yuan attacked the Duke of Tang, and after this, he gave birth to two sons, Li Boyi and Li Fengci, so as to "avoid" the results of two people, who were still officials during the tang gaozong period and were despised by li zhi of tang gaozong.