beyond the financial aspects have you considered the control issues?
what happens if you have a falling out with your parents and they change their wills?
what happens if the surviving spouse remarried and changes the will?
what is their financial position and what is the consideration of their nursing home needs? who is paying for that? the goal is normally to liquidate the estate not increase the size of the state if you want Medicare to come in and pay for the nursing home care ......
What it appears is that you are trying to take advantage of step-up rules at death. There are rumblings (google "step-up") that the step up rules could change or be eliminated under the Biden administration; under that scenario, it may be risky to upstream assets because the likelihood of the owner dying before another administration can change the laws back again increases (and the estate ends up paying tax that it may not have paid if the assets had not been upstreamed). This may be the biggest risk with the strategy you are contemplating.
