Maybe I can offer a liitle advice:
1) It sounds like you may have problems converting your license but I suggest that you go to your local Strassenverkehrsamt Des Kantons Zürich and they will be happy to tell you what can be done/must be done. Link:
www.stva.zh.ch
It's best to talk to them first before you make any plans so that you are clear about the situation with your license. If you have to take your motorcycle test in CH, then I would recomend that you do this as I think when/if you return to Singapore (or go to any other country) the entitlement to ride a motorcycle should be added to and remain on your license. (Hopefully, you will never have to take another motorcycle test)
2) Once you have sorted out your license, I strongly advise you to look at getting a bike over 25kw. For touring europe, I would say that a good starting point would be around 55Kw. Personally, I am about to buy something like a Hayabusa around 125Kw. (I like to get where I am going in good time!)
3) If your brother was to buy a motorcycle, then most insurances will have an option to allow any driver. However, be aware that even if he has full insurance, if you 'borrow' the bike and crash it the insurance will only cover third parties and they will not pay for any repairs to the bike. If you're lucky, they may transport it back to his home address.