I'm sorry, but I don't have any special knowledge as to how to help with the questions that have been raised.
I did find these names in the 1902 London Trade Directory - Hairdressers and Perfumers section:
RADISIC, Sebastian. 4 Canfield Gardens, Hampstead
RADOMSKY, Mark, 74 George St., Euston Square.
They may not be yours, but could possibly be spelling variants, so thought I would mention them. I got them from German Hairdressers in the UK by Jenny Towey, available from the Anglo-German Family History Association. It is an interesting read.
If you have time and access, you could trawl through the newspapers of the hairdressing industry at the British Library at Colindale; there is a lot of info in them, although I have not seen them. Methinks they are begging to be indexed.
If these people left wills, you might get a clue there, but more likely you would not.
What I have concluded from my own family history, now that I know as much as I do, is that in the wake of, first, one world war, and then another, with Germany being the enemy in both cases, and Austria, it was very common to downplay or camouflage one's origins - making them harder for us to find them now. Anti-German feeling, indeed hysteria, including a significant amount of violence towards Germans in England, led people to be quite circumspect. I have found this throughout the various families of German origin to which mine was closely related in the late 19th/early 20thC. They all acted like each other never existed, never mind their original families in Germany. I am quite sure my London-born grandfather understood German, but he never uttered a syllable, and his children never knew. You thought yours were French; we thought ours were "continental" - Belgian or Dutch, but certainly not German!
Something else you might look for is whether there are other people in England at about the same time with the same or similar surnames, coming from the same country. Don't pay any attention to family members telling you that there were no other family members who immigrated. Fully 3/4 of my family have emigrated from one country to another. What I have learned is that almost invariably they did not come alone. Sometimes it takes a while to find the brother (usually 1 or 2), sometimes the sister, and even the father quite often, but if you poke around, you will often find them. These other people may have more information attached to their names on some record or other.
Have you looked for naturalisation records? In most cases, they don't exist, and may never have existed, but worth checking, which you can do online at TNA. If you find one, order it; it will likely give details of origins. I found one out of the four men I was tracking, but it did not give his origins, which was very disappointing.
Hermine is also spelled Hermione sometimes, which may or may not help. It often gets butchered in transliteration, so search broadly.
Wish I knew more!
