The book,"The House of Waltman and Its Allied Families" by Lora S. Lamance states that Melchoir Yant b. 1707 came to America in the Ship Robert and Oliver, Walter Goodman, master, sailing from Rotterdam and landing in Pennsylvania, September 11, 1738. In this book it says Melchoir had three sons namely John, Jacob and Casper and that Melchoir's son John married a Margaret Waltman. John Yonce as he was named and his wife Margaret lived first in Lancaster Co., PA and later in Dauphin Co., PA. They had six sons namely Peter, Valentine, John, Conrad, Nicholas and Andrew. No birth dates are given but the author notes that Peter and Valentine (twins?)were about 19 when the Declaration of Independence was signed so they were born about 1776-19=1757.
Assuming all of John and Margaret's sons were born in the 1750s we can deduce that John Yonce, the father, must have been born in the 1730s. Likewise John's brothers Jacob and Casper, Melchoir's other two sons must have also been born in the 1730s.
Several Postings on this site appear to skip a generation and list Phillip, Valentine and John Yant as sons of Melchoir Yant. The birth dates given for these sons of Melchoir are in the 1750s suggesting that Valentine and John, at least, would appear instead to be the same named sons of John and Margaret Yonce. This seems more logical because if Melchoir was the father he would have been in his 40s and been living in America for over 10 years before they were born. The only problem with this conclusion is that Phillip is not mentioned in the House of Waltman book as being the son of John and Margaret Yonce. Perhaps Phillip is the son of one of John Yonce's brothers Jacob or Casper.
Luther V. Yonce in his book,"Yonce Families in the United States of America" lists the birth dates of Melchoir's sons as John Yonce b. 1734 in Germany, Jacob Yonce b. 1736 in Germany and Casper Yonce b. 1739 in PA. He indicates that both John and Jacob accompanied their parents when they immigrated to America but doesn't cite the source of his data. I have checked the passenger lists of the Ship Robert and Oliver on which Melchoir came to America in 1738 and he is listed as Melchoir Yand. Unfortunately, the ships list only includes the names of the 106 men who sailed on the vessel. The ship's manifest notes that there were 320 passengers on the Robert and Oliver of which 106 were men and 53 women for a total of 159. That leaves 320-159=161 other passengers which must have been chilren. It is therefore entirely possible that Melchoir's sons John and Jacob did immigrate to America with their parents.