Normally it's the vehicle that's insured (for any driver (with possible restrictions)), and not the driver.
I drove my SiL's car when on a visit, before I moved here (many years ago, though - things may have changed).
A quick call to your insurers will confirm.
.... and regarding which car, it will depend on how much experience he has on left-hookers, driving on the right, which you feel most comfortable providing. More insurance is good.
Personally, I'd give him the crap car and see if he can supplement his holiday insurance with some kind of third party liability add-on, to cover anything that the vehicle insurance may not.
This is what I thought .. There's no mention of 3rd parties driving the car in the insurance documents and it's just what I always thought, i think the insurance company told me this originally when i asked them to add my wife to the policy, although she's obviously resident here
My little doubt was that CH residents have (well usually have) 3rd party insurance for themselves and visitors generally don't.
So I think basically vehicle/property damage would be covered by the car insurance.. And personal claims would be on his head.
Obviously, if you only got third party or a large franchise- then it might be a good idea to decide in advance who would pay what. And of course if they drink and drive and get up to excessive speeding, dangerous driving- then insurance might choose not to pay as per new rules. Depends how much you trust them.
just in case your still in any doubt john, to back up the others i also have my brother drive over here because its the same as said previously: in switzerland the car is what your insuring.
check of course, but it's a fairly consistent message it should be fine.
Just a word of advice. If your foreign resident friend is about to enter his own country of residence with your car, he should stop at the border and declare what he is about to do: Temporarily importing, for usage, a valuable good on which no tax nor duty was levied in intended country of use.
They my grant the use (some fee may be levied for paperwork) or deny the usage. Not stopping at the border could be a tax and/or duty violation. Car my be seized and impounded and only released after any duty, tax, and fines due have been paid which may be a multiple of the cars actual value.
Don't know how old your younger brother is but I know on my policy there is a restriction on under 25s driving regularly ("regularly" is not precisely defined). I had to pay extra when the minis were younger than that.