That's fine, Hannah, I understand
I would just stick with the real royal family - their names at least, since they will be familiar to the children reading it, and provide the correct historical setting.
When it comes to fantasy you can put real-life famous people into any situation you want, and your tale could easily provide an alternative cause of death of Prince Albert. (Or, since it is set in the late C19th, threaten the life of the heir apparent, and others waiting in succession of the elderly Queen).
(cf. Susanna Clarke's unique take on the Napoleonic wars in Jonathan Strange & Mr Norrell).
- NaomiM
<Added>An alternative would be to make up an offshoot royal family and find a loop-hole in the succession to the English throne; someone who would have a legitimate claim when Queen Victoria died - maybe someone who's fiance is a catholic and is prepared to give up the crown to marry him - but the baddie steps in to try to prevent that, and so grab the English throne.
<Added>That should be '...give up all rights to the crown...'
<Added>'...and make up a loop-hole...'
- my brain's addled too :)