Since my Mom passed I now have all her clothes and have been trying to get this odor out of them. It's on everything, even socks.
Only thing I can think of is Mom used a detergent that had a heavy scent, then used a different scented fabric softener, thus it created a strange smell, like a science project gone bad. Being she was in her 90's she probably couldn't smell it, neither could my Dad.
Now that I think of it, for the past 6 years Mom would give me the grocery order and the same detergent and softener was always on the list. So that means more than 6+ years of using the same products. Any magic potions out there?
If the clothes are synthetic, it may be harder to get the odor out as I've noticed that some of the synthetic blends just don't clean that well, especially if stains have set, and it maybe that odors set in synthetics the same way.
Another factor may be that dryers have set in the stains. I was reading up about getting mildew stains out of some blankets I had used in the car and learned that. I don't use a dryer; everything I have is air dried (to reduce my carbon footprint) but I do recall that dryers can set stains.
Good old fashioned sunlight could help, but not at this time of the year - too cold to be hanging clothes out!
My Mom only used her dryer for a few minutes on each load of clothes, then she would pile the damp clothes into the laundry basket and take them down into the basement to hang on the clothes lines. She did this up into her mid 90's.
Next time I try to wash her clothes [using the suggestions above] I will try a lower heat on the dryer. Half I am donating, I just want them to smell fresh.