What is this money you speak of?
I mean... is it $10,000 of savings, but irrelevant to their lifestyle because they have $30,000/year of Social Security vs a $25,000/year spending rate? $1 million in cash accounts, but they are happy because the dividends on their $2 million index fund covers the cost of their $25k lifestyle comfortably even though they have no Social Security? $50,000 of cash, but their three debt free rentals have positive cash flow that combined with Social Security exceeds their spending, yet to them its purpose is to cover repair costs, so they want the cash to be stable? Is it excess, or part of their plan for covering living expenses, in other words, and what is their default plan for using the money, and what role does it play in their plan? What % of their total assets is this "money"?
I guess I'm saying that a good answer to your question depends on what your parents' spending rate and future needs are, what their assets and other income streams are, and whether they have any debt, as well as what their own goals are. Investment decisions should consider all of these factors. Please explain.