Hi Debbie I don't know for sure, but from what I can come up with is that the Nyssens were from an area of Long Island called "Midwout" which means Middlesworth in english.
One of the ways surnames were picked,was where they were from,and the dutch used the name of van"meaning from" so the name van middlesworth. I have seen the name spelled as one word "vanmiddlesworth" & van middlesworth and also just "middlesworh".
Denyse, I believe to mean " of nys" with the "de" meaning of (french)
Tunison, I believe to mean "tunis son" or the son of a man named tunis.
Their are sites on this forum for all the spellings of the (3) surnames
you mentioned that you came thru Denyse Denyse, I came thru his brother Daniel, his grandson ended back in New York state near Rochester and then one of his children moved to Michigan in 1859 and thats where I live.