How to Care for 95-yr-old male with edema?

He is a candidate for oxygen, but see a doctor first. Diuretics are not that expensive. Consider that he may also be ready for hospice

Your profile says that you live in Uganda. Do you have access to good health care there for your grandfather, because he really needs to be seen by a good doctor? His oxygen level is way too low and he needs to be put on oxygen ASAP, before the lack of oxygen does permanent damage to his vital organs.
And he should be on some type of Lasix medication for is edema.
You can try and keep his legs elevated to try and decrease the fluids in his legs, but realistically he needs to be taken to your nearest hospital.
If you don't, he more than likely will die sooner than later.

I checked your profile and see that you are in Uganda. Edema could be a sign of heart failure. Please get your grandfather to a medical facility as soon as you can.

Ask his primary physician right away. This condition isn't for amateurs.