What does Victoria having a child have to do with anything?
Your conspiracy is based on hiding a son to have Victoria on the throne to separate the thrones.
However, Victoria's heir from 1837 - 1840 was her uncle, who also had a son so if anything happened to Victoria while having a child then the whole conspiracy fails as they are back with combined thrones.
The Duke of Cumberland - who became King of Hannover - also wanted to be King of Britain and would have been delighted to have both crowns.
Had Victoria died in childbirth and the child with her then the King of Hannover is again the King of Britian and thus your conspiracy about hiding a son to separate the thrones is totally flawed.
I will try to put it more simply:
During William's reign the line of succession was:
Victoria
Duke of Cumberland
George of Cumberland
Duke of Cambridge
George of Cambridge
Daughters of Duke of Cambridge.
So for your conspiracy to work they had to know when this supposed son was born that Victoria would successfully have a child to separate the thrones. Given the high rate of still births and deaths in childbirth that is not a given, for any woman at that time.
For the first three and a half years of Victoria's reign the line of succession was:
King of Hannover (Duke of Cumberland)
Prince George of Cumberland
Duke of Cambridge
George of Cambridge
For these years the next in line after Victoria were all male and would have re-united the two thrones again.
The only way to stop the re-unification of the thrones, assuming your conspiracy is right and I don't for one moment believe it, was for Victoria to have a child and that wasn't a given.
Far easier, to pass legislation, which George I would have supported by no later Hannoverian King would do.