$1M unused 529 Plan - What to do

Hi, 42F NW $20M. I have a 529 plan from 40 years ago that was never used, now valued at \~1.3M. I have three kids under 10 whose 529 plans are already around $350k, I think the max cap on them is $600k. (I realize we should have funded their account with my money, but we overlooked it). I looked into ROTH IRA rollover but the max lifetime contribution is $35k, which will not help me. At this point, is it worth just holding on to this thing until my kids have grandkids. (That will not be for about 20-25 years though). The alternative is maybe the law changes in that time period? It's hard for me to justify taking the distribution given tax bracket and penalty, considering I do not need the liquidity. I had one outside the box idea. I have three siblings, 2 have children with fully funded 529s as well. I do have a sister who is just married and expect her to have children. Once she was done having kids, say three, I could then use my $1.3m to fund her children's 529 plans, and then I would have her give an annual gift to each of us in our family. $100k/year. In 10 years we could get there. Just typing this out seems way too complicated. I sound screwed. Thoughts. PS It is kinda crazy the IRS doesn't allow for donations either from the plan.