@januaryjane
I feel for you as I know how hard it is for adult children to deal with parents/in-laws with dementia. My mother in law had Alzheimer’s and I know how stressful it can be for caregivers. I did more of the caregiving because her son (my husband) was in denial and did not want to accept or fully understand her diagnosis and condition. I kept bugging my husband to do more for his mom but he was very slow in getting her in home care before she ended up in a nursing home (she started to wander and my husband and I both worked full time and had a toddler/young child during her diagnosis/decline.

The best advice I have is to do as much research as you can to understand the condition and how best to care for yourself as a caregiver to avoid/minimize burnout/stress. You need to go through a grieving process throughout the disease as you lose more of your parent over time. It is really hard to watch the disease take over the person you once knew.
1. https://www.medicalnewstoday.com/articles/how-to-deal-with-dementia-parent
2. https://www.chaptershealth.org/chapters-of-life-blog/medical-conditions/10-tips-for-dementia-caregivers-expert-advice-from-clinicians/
3. https://www.healthline.com/health/dementia/what-to-do-when-you-think-a-loved-one-has-dementia
4. https://www.healthline.com/health/dementia/caring-for-parent-with-dementia-at-home
5. https://www.carewell.com/resources/blog/how-to-talk-to-a-parent-with-dementia/
6. https://neuraleffects.com/blog/how-to-help-a-parent-with-dementia/
7. https://stagesofdementia.org/blog/how-to-help-a-parent-cope-with-dementia
8. https://seniorsafetyadvice.com/how-to-talk-to-a-parent-with-dementia/
9. https://www.humangood.org/resources/senior-living-blog/how-to-cope-parent-living-with-dementia
10. https://www.healthline.com/health/dementia-change-in-personality