Can Low Blood Sugar and Too Much Water Decrease EFGR?

3 months ago spouse's EFGR was 35. Test taken yesterday indicates it decreased to 29.

He is diabetic/high blood pressures.

He has been working on stabilizing his blood sugar. It can have a swing up to 200 and then severe drops where he is starting to crash at 60.

The nephro has prescribed additional BP meds in addition to the Lisinopril. She added 5 mg Amlodipine which didn't make a difference and then she added another 5 mg. Which still does not seem to make a difference.

He drinks at least 64 oz of water daily.

He does have a low urine stream and I believe the doctor had shared that he had an enlarge prostrate.

Now to my questions:
1. Can he be drinking too much water? The doctor had shared, stay hydrated!
2. Can the sugar crashes be as harmful as high blood sugar? His glucose number that was part of the same test was 47.
3.) Can the reduced flow of urine case the EFGR to drop?
4.) Anybody have experience with Amlodipine and not working?

We have an appt on 2/3 with the Nephrologist, which I intend to ask all these questions to. But was hoping someone here might have experiences/knowledge to share.

***Sorry for the long post. I wanted to give a background.

Any ideas/information would be very helpful.