Firstly, the then widowed Queen Marie of Hanover got an allowance out of this fund, later Kaiser Wilhelm II made sure that the interests were paid to the Hanoverian family.
Queen Victoria had an ambivalent relationship to her Hanoverian relatives. Moreover, she was the proud mother and mother in law of the crown princess and crown prince of Prussia. In the end, Victoria was in no position to really help the Hanoverians politically. There are letters from her and her cousin the 2nd Duke of Cambridge, then third in line to the Hanoverian throne, discussing these things.
But Prussia clearly considered the family relation, and would the last Hanoverian King Georg V have accepted the situation, he and his family would have enjoyed their German fortunes without any disturbance.
Apart from that, the Hanoverians had huge financial assets in Britain (at least Ė itís hard to find out). They were a very rich family so in no need for financial support from the Queen. They bought property in Austria, their land of exile, extended and constructed vast palaces and castles long before the new financial solution under Wilhelm II.
The Prussian Kings/Germans Emperors made use of the Hanoverian palaces and castles that were considered state property, but they had to bring their own furniture. Other palaces and castles considered private property kept untouched:
In a book from the 1920s/30s an art historian describes his visit to the summer palace in Herrenhausen, which was private property. The rooms were literally untouched since the flight of the royal family in 1866 Ö