From my newest digital instructor manual (recieved last month);
The maximum inwater ratio for confined water scuba training is 10 student divers per teaching status padi instructor, with a certified assistant required for each four additional students.
For open water training, 8 students per instructor, 10 with a certified assistant or 12 maximum with two certified assistants.
With 10 - 11 year old students, maximum 4 students per instructor in open water with maximum 2 ages 10 - 11.
The ratios in the op are within standards for confined water, unless both DMs were off with individual students (13-1)?