My deepest sympathies with what you both are going through. My worst nightmare. I agree with the no need to make a decision for a few months.
I also agree that you may as well file at 62. The “smaller sooner/larger later” argument is still valid. As to his, the when discussion is still as complicated. The claim sooner and invest it for a longer term payback vs the delay later for highest “pension” is also still the same. From a strictly numbers standpoint, it depends on if there are other sources of income, and how the current nest egg is invested and how comfortable the OP is herself with investing. A person that handles things very conservatively vs a market investor are in different potential playing fields.
On going Chemo & radiation will be expensive even with Medicare and the deductible long gone. Out of pocket treatment costs can EASILY become $10-15k a month.
Unfortunately I have had too many friends that discovered this with different cancers. I have no knowledge whatsoever on the OPs DHs potential costs, but this should be addressed once they are undertaking a plan. It may make more sense to file sooner to prevent too much early reductions to the investments, especially if the OP has investments that have suffered during the current pullback of the market, but was expected to recover through time, or their investments are earning currently high interest rates which may get reduced later as inflation drops/market improves and rates are reduced.
The tax situation will change as suddenly filing itemized will be needed to include the medical deduction. So increased taxes that may occur from claiming SS earlier will more than likely be a non issue. Putting off filing for his until the OP FRA is still good advice.
My point is that perhaps not filing until his age 70 or forced earlier, may take many more years to recover the impact to the nest egg because of the lost opportunities for tax relief from excessive medical costs and the effect on drawing down the nest egg. In addition, many people, if health allows, will want to “do something while Instill can”, IE a lavish vacation, whatever, which while further impacting finances, may be the only Ray of sunshine the suffering person and spouse may have together. After all, life is to be enjoyed and is the reason we live. Delaying as long as possible is usually though of with business as usual conditions, not under the unusual condition currently discussed.