Put the funds into an account in your parents’ name or maybe one of your siblings if they are trustworthy, not yours. Why ? Because if the account is in your name, the gubmnt will consider it assets that can be used for your kids’ education and it will reduce the amount of financial aid for which they can qualify.
I was just at a college financial aid meeting. When the presenter said this an audience member piped up and said “Why didn’t you tell me this when my kid was 4?” So, I’m telling you now.
Read all about FAFSA and the ECA and you’ll know what I mean.
As FLU says, if you have 5 rental properties, financial aid is out the window anyway so maybe not important.
I’d consider setting up a company to manage those 5 rental properties, make the kids an employee of that business, give them a little salary on which they will pay tax at the below-poverty rate, and the business can pay up to $5200 of their tuition tax-free on top of that.