It seems to me that the person actually asking for money from retired parents who can't afford it (the husband) is the bigger problem. Maybe he has a hard time saying 'no' to his spouse, but it's a word he should learn, use and not give in to entreaties.
Even if his parents were generous with him before they retired and began living on a fixed income, he should realize it's unfair to use them as ATMs at this stage of their lives. It's time for him to stop the practice of approaching them with his hand out. When one's parents are retirees, it's stand-on-your-own-two-feet time...or should be.
You don't mention the couple's ages, but some people are mature at handling their finances in their twenties while others haven't gotten the hang of it by their forties. I think the public school curriculum should include a required class in middle school that teaches kids financial skills and fiscal responsibility so they're prepared for adulthood. Such a class would be immensely practical.
Both the husband in this situation and his spouse should do whatever is necessary in order to meet their own financial needs without asking family or friends for monetary donations or loans unless it's a real emergency. If running short of money (or simply wanting more than they have) is an ongoing problem for them, they may need to consider change at two levels--(1) saving money and (2) earning more of it.
In today's economy, people of all ages and varying incomes are learning to budget (if they didn't already know how), living more frugally, preventing waste, avoiding overuse of credit cards, and doing without things that are luxuries rather than true needs.
Changing jobs, getting temporary part-time (second) jobs, acquiring more education or additional training to prepare themselves for promotions/raises are all ways to increase income. The bottom line: a married couple should accept responsibility for themselves and not depend on parents for solvency or extra spending money.
The retired parents have an opportunity here to teach their son one more life lesson by saying 'no' to his requests for money and explaining the reasons for their response. He can pass the lesson along to his wife. Here's hoping they both understand it.