I can speak a bit to gifting, but you didn't mention plans for Long Term Care, so let's discuss that first.
So Medicare is insurance for the elderly (two parts, as noted earlier). Part B you have to choose among several options and enroll in a timely manner or you get penalized. Part B is not free, so your parents will need to assume that a chunk of the SS they have been promised will be deducted to pay for whatever part B they choose.
BUT, Medicare doesn't cover long term care or nursing home costs at all, except for limited periods in nursing home or rehab centers after Medicare covered surgery, etc. This is a big problem and most people fall into one of several categories...Low/Middle/or High assets/cash flow.
Actuaries probably have run numbers that I'm too lazy to look up, but elder planners usually seem to advise that if you have assets above 1 million in retirement or a large enough monthly cash flow, you might have enough to 'self insure' (pay for any LTC you might need out of pocket). Depending on whether you have in-home care vs nursing home care, and what state you are in, it runs 100$-400$/day (so not unheard of to cost 150K/year). About half the population will require LTC for some period of their lives, and the average time spent in LTC is a couple of years. Of course, averages don't mean a lot if you get situations like early onset Alzheimer's...then it can be a decade or more. And some people never need it at all. You see the challenge?
For people in the mid range of assets/cash flow (maybe 350K to 1 Million), most financial planners recommend that people consider buying LTC insurance, but it is limited in the scope of how much it will cover, how long it will pay out, and it is relatively expensive. Most companies do not have fixed premiums, which means premiums can be raised under some circumstances. It sucks. Most actuaries suggest that if you are good health, the best age to buy is mid to late 50s, but you have to look at your own health history, etc.
If you are relatively low-asset/limited cash flow, most financial planners will assume you will exhaust your assets paying for LTC until your estate is gone and you are poor. At that point, you qualify for MediCAID, and the state will pick up the cost of LTC. There are tons of rules governing qualifying for Medicaid, and they vary from state to state, so this needs to be investigated. In WI, my grandparents had a very small pension (maybe 500$/month, and about 2000$/month SS, and no assets except a modest house worth about 180K). They had a couple of very small life insurance policies, which put them over the limit in assests, so they had to cash them to qualify. My grandfather went to a nursing home for 'free' for a couple years until he died, while my grandmother lived in the house and retained their small monthly income. At that point, I think her bank account had grown so she was a little bit over the qualifying limit of assets. So then her kids had to spend about 8K on 'personal items' (clothes, personal care products, etc....their are rules governing what can be bought) to keep her qualified for Medicaid.
*NOTE: There are people on this forum that will yell about the ethics of this, and that is certainly something that everyone has to grapple with and decide for themselves. However, it is legal, if rules are followed, and is often advised by social workers/Medicaid specialists when you are poor and that close to qualifying for Medicaid.
Anyway, grandmother was in nursing home for about 5 years. When she died, the house was sold and the state took the proceeds as 'payment'. There was nothing for the kids to inherit.
Finally, this leads me to your particular situation. Your parents seem to fall into that tricky middle ground of assets/cash flow. They have quite a bit of money, but will it be enough to pay for LTC for one or both? If one person needs care, it can devastate the assets of the remaining spouse, since most states require only leaving the house and about 100K of assets for the remaining spouse to live on.
On the other hand, if your parents haven't purchased LTC insurance, it is likely really expensive to get at their age.
So....gifting. If they do not have LTC insurance, and suspect based on family history that one or more might need LTC, they need to look into the cost, and consider how long their estate would last if they had to pay for it BEFORE gifting any money, which they might need later.
However, they might be the type of people who sort of shrug and think: oh, well...if I end up spending down assets, that's just the way it is and I want to gift money now. In that case, they need to consider the TIMING of gifting. If there is any possibility that they will be needing Medicaid for LTC (remember, they will need to be pretty poor to get it), there is a look-back/claw-back period (5 years I think, might vary by state) from the date someone first applies for Medicaid. The state looks in detail at the applicant's financial records, and if any money has been gifted to charities or family within 5 previous years, the Medicaid will NOT kick in to cover LTC costs until that equivalent amount is paid by the applicant.
This is done to prevent very wealthy people from gifting ginormous estates to their kids and then going on the state's dime for 'free' LTC.
*NOTE: Again, gifting down an estate is perfectly LEGAL, and is sometimes advised by financial planners depending on the situation, but your ethical comfort with this is more of a personal call.
In summary, if one or both of your parents anticipates being poor at end of life and using Medicaid, then gifting, if done at all, should be done carefully, and the look-back period should be considered (for example, the gift recipient might consider prudently not spending the gift money until the look back period is up, in case it should be 'clawed back').