Hi Louie,
Great, work together and do some research on MF. Syndication is a good place to start if he doesn't have experience. Partner vetting, and finding deals in strong markets, conservatively modeled / assumptions and experienced team are important. Here's a few articles to continue the learning process. I'd also advise looking at spreading some of that into multiple syndicates, geographies. Value add a must. There are other types of niches that have fairly good "all weather" holdings such as mobile home parks and self storage. It all starts w/having a strong operator, doing your homework and patiently moving into on opportunities. These are fairly illiquid asset holdings so make sure he understands that as well.
With this much capital, he might even be able to play into the GP side of things as another angle. With proper vetting of sponsor, even look at leveraging this wealth by being a guarantor on a non-recourse loan to gain GP fees / equity.
Vetting a sponsor, why I like investing in large apartments and 25 FAQs on syndication......happy reading.
https://www.biggerpockets.com/blogs/9145/53820-why...
https://www.biggerpockets.com/blogs/9145/53959-vet...
https://www.biggerpockets.com/blogs/9145/65780-syn...