Thank you for the questions.
Grouping symbols around fractions that are transcribed spatially are not enlarged [because they do not enclose multiple separate rows of information]; they are transcribed using simple one-cell grouping symbols on the braille line with the fraction indicators and fraction line.
See the fraction transcribed spatially in the denominator of the second example on page 79 of the Nemeth Code [section 68’s example (3)].
In response to your second question, section 60 of the Nemeth Code says in part, “Items which are individually canceled in ink print must be represented as individually canceled in the transcription.” Unfortunately, there is not a way to transcribe your print’s one long strike that cancels both one fraction’s denominator and a separate fraction’s numerator. So, yes, simply cancel each appropriate numerator or denominator on its own.