Hi Defor
I'll be passing St Mark's on my way to the Archives today. Here's a picture of it
http://www.wishful-thinking.org.uk/genuki/GLS/Gloucester/StMark.htmlUnfortunately it closed recently, though it has now been let out to a mission church. There could be a problem however, in that this Church was built in 1845-7, and you don't say when the Spire marriage took place, just that they were found in Barton Street in 1851. Did they marry in a brand new church, I wonder, or was this church built on the site of a previous St Mark's? I'll take a look at the parish register to find out.
St Mark's Street is some quarter of a mile away from the church, but I've never heard of Brother's Place. The only new building (i.e. 20th century) I can think of nearby is Gloucester's only tower block with surrounding houses and flats, just behind the church, so maybe Brother's Place is beneath that**, but I'll enquire at the RO. The name does suggest a link to one of Gloucester's five monasteries/priories. The ruined St Oswald's Priory isn't all that far away and neither is the Cathedral.
Barton Street is a mile or two away from the church.
I'll report back later with what I find.
Gill
**Or it could be under Gloucester Rugby Club ground, of course. That's almost opposite St Mark's.