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.
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.
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.
They are more risky than your average equity fund. Investments like these you need to hold for at least a decade.
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.