I’d see a lawyer before moving ahead.
Are there other children, grandchildren/heirs? Are they onboard with the grandparents kicking in 100K for a home in which they have no equity interest? Are they onboard with the grandparents kicking in for monthly expenses? What happens if the housing market takes a tumble and the value of the house declines- but you need to sell for some reason- wage earners lost their job, need to move for a new job- are they going to claim that you “owe” the grandparents “estate” the 100K (which may have evaporated if housing prices decline)?
Get some professional advice here (not a mortgage broker) before moving ahead. From what I’ve seen with some of these senior living/family arrangement situations, financial aid is the LEAST of your potential problems!!! Your parents need up to date wills; you need up to date wills; you may want to put the house into a trust; there are a lot of considerations here.
And the current limit on annual gifts is 15K btw, went up from 14K in the “new and improved tax plan”.