Help! What is wrong with my dog? Tremors, convulsions, weakness, confusion?

Описание: Our baby doxie is over 100-dog-years-old. And for the past few months started peeing more frequently than we could get him outside for. Now we have to go out every two hours. We thought he might "just be old;" but it's more than that, clearly. We thought maybe it was diabetes -- nope, normal glucose. And then maybe an infection -- none specifically apparent, but not entirely clear, yet. [Note: We're in the middle of moving, too, hence junk all over the floor in this video.]
His coordination is disintegrating fast! Three weeks ago, he seemed mostly normal — a little clumsy, or unsteady -- noticeable, but not radically alarming.
He stayed at the in-laws for a week, and now that I have him back, he is totally having these blank stares and shakes — like there is a storm in his brain. Definitely alarming now. It is more and more frequent: almost nonstop sometimes. He stumbles when he walks or stands still, can't climb and starting to bump into walls and walks into weird areas. He wanders around in the evening, and eats a lot -- kind of strange and semi-conscious behavior. I'm happy he is eating -- but still, so sad 😭. He was almost always such a happy, healthy, energetic boy.
His blood and urine tests so far seem normal except elevated BUN/ Urea ratio of 43, which is higher than range of 9-31. Probably something related to his kidneys.
But otherwise he is eating and drinking fine — too much, really. Is very strange. Like his mind is coming unraveled. The vets do. It know what this is. We are desperately trying our last hope of hopes with pills for seizures, antibiotics, and some kind of dog hemp. He seems healthy, except his nerves or brain are seizing up and shutting down. I can’t understand it. No sign of pain, except around his kidneys he is sensitive — just confusion and discomfort with these constant "spells." It’s so terribly sad. Any serious analysis is welcome. I’m afraid he does not have long.
My sweet baby has looked after us for so long, and it may be his time to go -- but it seems like there might be something we can do.
Urine tests were said to be normal, no significant sign of bacterial infection. He is not diabetic. His blood tests are all normal except:
BUN/Urea 43 mg/dL [HI] (ref 9-31).
ALB 2.8
ALKP 42 U/L
ALT 86 U/L
Anion Gap 18 mmol/L
AST 36 U/L
Bicarb 23 mmol/L
Ca 10.1 mg/dL
Chloride 1114 mmol/L
CHOL 239 mg/dl
CREA 1.3 mg/dL
DBIL below 0.1 mg/dL
GGT 11 U/L
GLU 87 mg/dL
IBIL 0.0 mg/dL
PHOS 4.1 mg/dL
Potassium 5.3 mmol/L
TBIL 0.1 mg/dL
TP 5.9 g/dL
Sodium 150 mmol/L
A/G Ratio 0.9
B/C Ratio 33.1
Na/K Ratio 28
GLOB 3.1 g/dL
CK 130 U/L
SDMA 11 ug/dL

The doctors have made many guesses, but mostly want us to run more tests like MRI and ultrasound, which costs more money than we have, unfortunately.

The 3rd vet has given us some last-effort meds, I guess:

Orbax (Orbifloxacin) -- antibiotic

keppra levetiracetam -- an anti-epileptic drug

VF Bio-Dent -- supplement for his teeth, I think, may have a dental problem

pH-notix -- Ear wax cleaner: Says he has build-up in one ear, and a perforated ear drum in the other. Don't know when or how that happened.

CannaCompanion -- "Neurological health and of life care" hemp for dogs.

I don't know what to do for him; since we have no specific diagnosis. I guess we give him these pills. The antibiotic is messing up his belly already, as expected. Poor thing. No idea if we are making him better or worse -- but we feel like we have to try something while we still have a chance. He still loves cheese, for sure. And we love him so.