That does not say they sojourned in Egypt 430 years. It says of the children of Israel who had lived in Egypt that their total sojourning had been 430 years.
It seems to me that you are assuming that Jacob's other descendants went down to Egypt before Jacob did. Only Joseph lived in Egypt for around 35 years before Joseph saw his brothers on their first journey down to Egypt to get Grain, when he was around 52 years of age. Joseph only lived for another 52 years before he died, and Levi survived him for another five years or so. All of Jacob's sons died around the same time period. This information was established from the stories lines in the Book of Genesis but the scriptures are relatively silent as to when Jacob's sons were born or how old hey were when they died.
Now whether or not the chronology of the descendants of Levi is complete in the scriptures is debatable and your argument is from the silence of the bible. Others claim that there were only 4 descendant generations born while they were down in Egypt, but the Chronology of the descendants also list up to 10 descendant generations being born in Egypt as well.
We must remember that only information relevant to the Salvation Covenant Story was recorded in the scriptures.
Sometimes it is just as important to for us to graciously accept what is recorded in the bible and not try to dot every "i" and cross every "t" so that we have something definitive to believe in. We must take the bible stories by Faith.
Shalom