I have just found this site and as a descendant of Robert ALLEN organ builder, I have a few comments to add and some corrections.
Robert was apprenticed to Father Henry Willis who sent him to Winchester to overlook the installation of their new organ. As a result, my great grandmother was born there. He then returned to London until 1859 (as you said). He then purchased the company in Bristol from John Smith who was a Moravian. Robert had a total of 9 children, not 7.
As for William. he was NOT the brother of Robert ALLEN Sr and he was NOT a shoe maker. He actually died in 1833. His Will and Probate was published 11 Nov 1833 and he leaves money to his son John and his son Charles Arthur ALLEN was one of his executors. This William was the Church Organ builder which was mentioned in his Will and he was baptised 09 Apr 1783 at St Marys, Walton on Thames the 6th of 9 children.
Going back to Robert 2 of his children were born in London and 6 in Bristol as well as Emma Elizabeth who as you say, was born in Winchester. 3 of Robert's sons were also Organ builders but all 3 died young Robert Franckling ALLEN age 51, Walter age 42 and Christopher John age 32.
"Willis was completing one of his first important organs at Winchester Cathedral in 1854: it had been built for the Great Exhibition in 1851, but very much remodelled for Winchester, so it would have been a big job: Willis's men were evidently there for almost the whole of 1854. Installation began in January, but when it was first heard in June the press observed that quite a lot was still silent: the official opening recital was not until November."
I have birth, marriage and death certificates as well as Wills.