One of the most important things is open communication with the parents. Try to persuade them to fill out LPAs and if they refuse then Encourage them make a living will. The way to sell this, say to them
"You need to be in charge of your own future, even when you don't have the physical or mental capacity to do so. Let us know now what you want in terms of your care and if an 'end of life illness' is diagnosed"
Secondly, and this may seem hard. You have to put yourselves and your children first. So many of us feel guilty, run ourselves ragged, and neglect our own health and families. Caring for the elderly is a long hard slog. People live well into their 90s and become more depended as they get older. Sadly not all of them are sweetness and grateful. Set boundaries and stick to them.
As they get older, you will find yourself dealing with Utilities, LAs and Health professionals. This is advice I have given many times on here but it is a life saver.
Make a record of every conversation you have with officials, about them. Name of perso you spoke with, time, date, and what was promised. Not one thing will get resolved with one phone call. Being able to quote back previous requests really helps.
Before things get really bad mentally, and if they are willing make a file of the following.
Their financial status, where accounts are held. Encourage them to simplify, sell shares, consolidate accounts. Luckily my Stepfather made me a joint account holder which made things easier
Details of Utility companies, insurance, LAs . Check that they are not paying unnessaey things. Car insurance when they longer drive, too high house insurance.
Personal details. dates and places of birth and marriage, mother's maiden names. Believe me , you will be asked again and again!
Medical history. Doctors details, hospital appointments, medication. Try to get a prescription list as this will help if you need to claim Attrndence Allowance.
If they will allow you make copies if any paperwork they have, so that you can deal with things remotely. I found Utilies often asked to speak to the person themselves if you are trying to change tariff, arrange a visit or get insurance cover. Have someone with you to pretend to be the house holder, otherwise you have to be in the house when the arrangements are made.
When things get so that they cannot manage, get a redirection of mail form completed. Again in helps cut down visits, and you keep control. You can see what is being spent, what appointmemts are needed etc.
AGE UK produce many leaflets which deal with the practical side. It is worth going onto their site and mugging up on what your parents entitlements and restrictions.