Sifting out all the member submitted chaff from the extracted wheat on the IGI it boils down to the following:
William Turner married Elizabeth Kempster at Eaton Bray (3 miles from Studham) on 25 Dec 1852. Whether or not this is your William can only be established by either buying the marriage certificate from the GRO or checking the parish register microfilm at your nearest LDS Family History Centre, to get his father’s name.
I cannot find any children baptised to this couple in either Beds or Bucks, but they may not have been baptised or their baptisms may not be on the IGI. But no children from an earlier marriage were living with him in 1880 in Utah. It’s also worth mentioning that in neither his baptism entry nor his possible marriage entry was he called William Henry Turner – the Henry only appears in the US.
I cannot see them in 1861 – if the 1852 marriage really is your William it’s possible that they emigrated before 1861 and Elizabeth died in the US prior to him marrying Victoria Goodey (I am assuming William and Victoria married in the US as there’s no trace of a marriage in the GRO indexes 1861-1865, but it's possible I suppose that all the trees are wrong and they didn't marry in 1863, but later. After all if the trees disagree to the extent of either Barking Essex UK or Salt Lake City Utah then the date could equally be adrift). Bart and Sarah could even have joined them later. I have a couple of ancestors who converted to the Mormon faith and emigrated to Utah in the mid 1850s, and I found a lot of detail concerning them in an LDS Family History Centre on a CDrom and in book extracts on Ancestry (which I cannot now access as I cannot justify nor afford their World de luxe membership)
The 1900 US census gives the year of arrival in the States, which would help to pin down when William arrived there, but I don’t have access to this either. You could try a request on the Emigrants to US board for a look up in 1900
There’s a photo of Bart on
http://www.geocities.com/phillott/Bartel.htmIn 1861 there's a Victoria L Goodey 20 servant born Halstead Essex living in West Ham. This appears to be same person who the Americans have as the wife of William Henry, so at least she didn't emigrate until after 1861 - a Goodey website puts the emigration year for the family as 1864, so either this date or the Utah 1863 marriage date must be wrong
David