There's no way to force the parent to wear adult diapers but speak with them and let them know that they will feel more comfortable wearing the diaper and not having wet pants or wet clothes.
Or if they have fecal incontinence then they will feel better having the poop in the diaper instead of getting the poop all over their pants, clothes, legs etc.
You can't force the parent to wear adult diapers but you can try to convince them.
When an elderly parent or someone older than 4 years old needs to wear diapers it can be hard to convince those people to wear diapers.
Most people older than 4 years old will resist wearing diapers because they deem diapers as for only babies which is not true.
Diapers are for anyone who needs to wear them and I even wore adult diapers after pregnancy because I had bladder issues temporarily after the birth of my kids.
So I would sometimes not make it to the toilet so I started wearing those tape on adult diapers when I was away from a toilet or couldn't get to a toilet in time.
Diapers really are not all that bad to wear but sometimes it can be really hard to convince an adult to wear diapers.
Even though the adult diapers are diapers you may need to stop calling them diapers when trying to convince an adult or elderly parent to wear diapers.
Try calling them absorbent underwear and maybe try the adult pull ups and not the actual tape on diapers that they can usually easily put on themselves.
Not every adult will need to wear adult diapers but we all wore diapers as babies and it's okay for an adult to wear diapers as well.
Try explaining to the elderly parent that they will feel much better and cleaner wearing adult diapers instead of wetting their pants or wetting their bed.
And sometimes you might need to get your parents doctors involved in the issue and have them help explain to them they need adult diapers.
And other times you may not be able to convince them to wear diapers at all.