I thought I would jump in here to help a bit. I see Ann shows Julia as Julia LADD and I think she is correct.
familysearch.org has a death record for a Julia A. Vanhorn, died April 7, 1880 Shelby, Macomb, MI age 69 years 1 months 15 days born about 1811 NY widowed housekeeper died of heart disease parents Winfield and Hannah LADD it also asks for residence of parents which says NY (but whether that means they were still living or just that they had lived there I don't know - I suspect they were not still living as they would be pretty old)
familysearch is a free site so you can take a look at the entry there it is under Michigan, Deaths, 1867-1897
as Julia was widowed at time of her death I tried to find death for Tim - who must have died before 1860 as he is not in the census with Julia. The death database starts in 1867 so too late for him.
I just noticed at ancestry.com that Julia is listed in the census mortality schedule for 1880 which shows she was born NY as were both her parents. She died of disease of heart. she was a widow she died in April
so it all matches with her death records from familysearch
Also in 1880 in Macomb Co, MI there is a census mortality schedule death for a Charles Vanhorn, born about 1804 PA so I wonder if he could be another brother BUT I did not find his death in the database at familysearch
there is another database for deaths and burials between 1800-1995 but not sure how complete it is as he is not there either and neither is Julia
I also was not able to find a death for Abraham Van Horn (likely brother to Tim) Abraham was still alive in 1880 so should be in the 1867-1897 database ?
Charles Van Horn (possible brother for Tim) is in Macomb, MI in 1850 census with wife and several children. The eldest children born NY , the younger born MI which also matches with children of Tim and Julia. Also I noticed from the ages of Charles children that he and his family came to MI about 1838 and one child born 1837 NY, next born 1839 MI this matches pretty closely with Tim's children one born 1836 NY, next born 1839 MI so they also arrived about 1837-1838 to MI
There is a Benjamin Van Horn, age 76 in Chesterfield, Macomb, MI in 1850 census - born NJ living in the house of John Van Horn, 49 born PA
so possible father for Tim and another possible brother there is also an Alice with them, indexed as age 16, but in the image her age looks like 76 and she was born PA so possible mother there is another Alice in the family age 15 which is another reason to believe the 16 is wrong for the one.
In 1860 census Benjamin is age 86, still living with John, but in this one Benj. shown as born PA Alice is not there
Find a Grave has Julia's gravestone (free site)
AND also Tim's which shows he died June 7, 1854
it has a link to deaths of parents Benjamin and Alice - BUT they do not show how they know those two are his parents - it does seem very likely though.
Benj. died July 31, 1861 and Alice died June 5, 1859 (which explains her not being in 1860 census) Her maiden name is shown as HELYER/HILLIARD
There is a name shown for both the person who first created the entries and for the person who maintains it so if you contact one of them they may have more info to give you.