Brief Answer:
needs a few more investigations

Detailed Answer:
Hi
You have not mentioned in which context all these investigations were performed, but apparently there is mild stasis of urine in kidneys, left more than right.
However, not everyone needs surgery and not everyone has the same amount of obstruction through out life. Quite often the obstruction remains very stable and is well compensated while occasionally it gets worse. So a serial study every 6months might give a better picture than a set of tests done only at this juncture.
As of now, no anatomic dynamic pictures have been obtained. I suggest you confirm that the boy's serum creatinine is normal and if it is so, please get a test called intravenous pyelogram or a CT urogram which will demonstrate the anatomy clearly. This should be followed by what we call MCUG where we rule out other causes of mild swelling of kidneys such as reflux of urine back into the kidneys when the child is passing urine.
Circumcision is a simple surgery and can be done for phimosis once the child reaches 2 years of age or earlier if there are frequent urinary infections due to presence of urinary reflux disease.
Hope I have been of help.

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Brief Answer:
apparently not critical

Detailed Answer:
Hi
From the information you have given, things do not look like they are very serious.
After discusding with your btother, you can let me know if the child is feeding well, gaining weight as expected; does he have recurrent urinary infections; any fevers related to urinary infection. Are your brother and sister in law related before marriage?
As I suggested, you can get your brother to have the child's serum creatinine estimation done along with a complete urine examination, and if they are normal, request for a urogram and MCUG asap, the latter preferably under antibiotic cover.
Best wishes.

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