Getting the mortgage sorted is the top priority. His options are to change to a repayment mortgage or to start a savings plan such as an ISA, to cover the mortgage capital when it falls due.
He is in a relatively decent position, with a good salary, not much debt apart from the mortgage and still under the age of 30.
Schroder Tokyo's performance has been a little disappointing during the past year. But even so, it has been a consistent performer over the longer term and is still worth backing.
You should choose the same funds that you would invest in for yourself - if anything you can take more risk on behalf of children as the investment is over a longer term.
They are more risky than your average equity fund. Investments like these you need to hold for at least a decade.