The Investor's Chronicle published a top 100 funds (unit & Investment trusts) at the end of 2017 and I would think you are looking for something in the real or absolute returns section to begin your search.
https://www.investorschronicle.co.uk/top-100-funds/2017/09/15/ic-top-100-funds-2017/One fund they cast adrift from their previous year's selection is:
Standard Life Global Absolute Return Strategies (GB00B7K3T226)
I have held this for years and have only, yesterday, switched into something else since the amount I held had little influence in my overall fund portfolio.
The funds listed in this category are:
RIT Capital Partners (RCP)
Capital Gearing Trust(CGT)
Personal Assets Trust(PNL)
Newton Real Return (GB00B8GG4B61)
JPMorgan Global Macro Opportunities (GB00B4WKYF80)
Henderson UK Absolute Return (GB00B5KKCX12)
Invesco Perpetual Global Targeted Returns (GB00BJ04HL49)
I leave it there.
Also I would not be making a purchase of any of them without looking over the reports and kicking the tyres first.
If the in-laws are ultra cautious then cash or safe bank interest (less than full compensation limits in the event of going bust) is the best option and it has no fees.
Hope that is a start.
midgesgalore