2y, should take higher priority simply because it cannot be any further resolved or simplified

Bingo!

That is not the case with, say, 2(3+1)

It's the same thing, where y=3+1.

1/7y. Is the coefficient 7, or is it 1/7? i.e. Is that 1/(7y)

Yes, it's 1/(7y) as per the definition of Terms.

Either way, if that’s not the the standard understood by everyone

It's the standard in literally every Maths textbook.