You raise two queries -
> I wouldn't have thought of looking in Manchester as all the family lived in the Radcliffe/Pilkington/Prestwich area.
Lancsann agrees that the Collegiate Church was a popular place for marriages and suggests that it may have been cheaper than elsewhere. I think that Hardwicke's Act and Anglican Church law required that the couple were married in the parish where one of them resided. Lancsann shows "both gave address of Gt Ancoats St" which is fairly close to the Collegiate Church. People from a wide area around Manchester used the Collegiate Church for their marriage and it is a bit of a puzzle as to the reason. One reason I have heard is that being married in Manchester was something of an exotic place, just as today some people jet off to the Seychelles, etc. This gave rise to some Mancunians allowing their address to be used as a place of residence to permit marriage in the Collegiate Church, so it is quite likely that the true place of residence could be outside the Parish of Manchester. The question of cost seems to have related primarily to residents in the Parish of Manchester. If they married at a licensed chapel of ease to the Collegiate Church, then they had to pay the standard fee to the minister who solemnised their marriage and also had to pay the same fee to the Collegiate Church as the Parish Church. So, it was much cheaper to marry in the Collegiate Church.
> I don't understand why if the family are C of E there's one child Baptised in the Wesleyan Chapel and the rest c of E then later generations become Unitarian.
Marriage in an Anglican church does not mean that the couple being married were CofE, because the Anglican church is prepared to minister to all Christians. Baptisms can also be a bit of a puzzle. If you are not particularly religious and just want your child to be baptised then perhaps the nearest church would do. The Wesleyan Chapel was probably the nearest one at Radcliffe Bridge (in the Township of Pilkington) which would be near the north end of Stand Lane. The nearest Anglican church would have been St Thomas in Radcliffe on the other side of the river but not much further, though the official parish church would have been All Saints, Stand. There were other non-conformist churches in the Radcliffe Bridge area, Stand Lane New Jerusalem, Stand Lane Independent/Congregational, Chapelfield Primitive Methodist, Stand Unitarian, so there was quite a choice. Just as today, the reasons people go to church or change the church they attend, are many and often not obvious.
Hope this helps,
Jim Lancaster (Bury, Lancs.)