They can and should choose the fund(s).
But Vanguard has rock bottom fees and a good reputation.
When do they intend to begin using the funds? Is the money just an emergency reserve fund or do they intend to spend some of it every year? If they intend to spend it yearly, how much of it do they intend to use per year?
BTW... Another thread in the forum recommended Otar's books on the subject of managing retirement finances. It can be downloaded here for free for a limited time in pdf format. Click on the free download link to get to the page where you can access the book.
IMO - It is a worthwhile read.
otar retirement calculator