If God were creating each person separately, why would He give Adam and Eve, and Jacob, this responsibility to multiply?
We learn a little about how God works with humans from the way He created the animals. He used very similar words when He blessed the animals saying, "Be fruitful and multiply, and fill the waters in the seas, and let birds multiply on the earth." (Genesis 1:22) And, in Genesis 1:24, God said "Let the earth bring forth living creatures after their kind."
So, we see that God created the pair of animals and made them where they could bring forth after their kind. God did the same with humans. He specifically created Adam and Eve and gave them the ability to procreate, to fill the earth without His special intervention with each one.
One important thing to note: God allows humans to make mistakes and even to do wrong things when they procreate. One example is when the angels saw human women and chose to have children with them. Their offspring were not authorized by God, but were still created using the natural processes. Those offspring became very evil (Genesis 6:2-7). They became so evil that God destroyed them in the Flood. Only Noah was "perfect in his generations”, i.e. his lineage was traced back to Adam and was not defiled by the fallen angels. He and his family were saved from the flood and continued the human race.
God does not create ill, deformed babies. The physical, emotional, and spiritual deformities we have are a result of sin and were not created by God. (Deuteronomy 32:4, “…his work is perfect…” )