How to get max and min values in linux shell with multiple possibilities?

This shell script gets me the max and min values, but I would like to get those values and the associated students when there are repeats.

Code:

#!/bin/sh
Notamax=0
Notamin=0
alumneMax=''
alumneMin=''
while IFS=";" read alumne nota
do
	(( nota > Notamax )) && Notamax=$nota alumneMax=$alumne
	(( nota < Notamin || Notamin == 0)) && Notamin=$nota alumneMin=$alumne
done <notas.txt
echo "Nota maxima $Notamax ** Alumnos con nota maxima: $alumneMax"
echo "Nota minima $Notamin ** Alumnos con nota minima: $alumneMin"

notas.txt

pepe;5
marcos;7
marta;70
luis;70
ana;5

Actual output

Nota maxima 70 ** Alumnos con nota maxima: marta
Nota minima  5 ** Alumnos con nota minima: pepe

Desired output

Max: marta 70, luis 70
Min: pepe   5, ana   5

How could I achieve it?

This is both easier and more versatile with Awk. See also Bash while read loop extremely slow compared to cat, why?

awk -F ';' 'NR==1 { min = max = $2; mina = maxa = $1 " " $2; next }
$2==max { maxa = maxa ", " $1 " " $2 }
$2==min { mina = mina ", " $1 " " $2 } 
$2>max { max = $2; maxa = $1 " " $2 }
$2<min { min = $2; mina = $1 " " $2 }
END { print "Max:", maxa
  print "Min:", mina }' notas.txt

Your output format is somewhat noisy; I would personally prefer a less redundant and more machine-readable display.

The awk tag info page has links to basic learning resources. Learning the fundamentals of the language is quick and easy (give it an hour and you'll already have a good idea).

If we need to stick with bash ...

Making a few changes to OP's current code:

NotaMax=0
NotaMin=0

while IFS=";" read -r alumne nota
do
    (( nota == NotaMax ))                 &&               alumneMax="${alumneMax}, ${alumne} ${NotaMax}"
    (( nota  > NotaMax ))                 && NotaMax=$nota alumneMax="Max: ${alumne} ${NotaMax}"
    (( nota == NotaMin ))                 &&               alumneMin="${alumneMin}, ${alumne} ${NotaMin}"
    (( nota  < NotaMin || NotaMin == 0 )) && NotaMin=$nota alumneMin="Min: ${alumne} ${NotaMin}"
done < notas.txt

echo "${alumneMax}"
echo "${alumneMin}"

Using a pair of arrays and matching namerefs (namerefs require bash 4.2+):

NotaMax=0
NotaMin=0

while IFS=";" read -r alumne nota
do
    (( nota == NotaMax ))                &&               alumneMax+=("${alumne}")
    (( nota  > NotaMax ))                && NotaMax=$nota alumneMax=("${alumne}")
    (( nota == NotaMin ))                &&               alumneMin+=("${alumne}")
    (( nota  < NotaMin || NotaMin == 0)) && NotaMin=$nota alumneMin=("${alumne}")
done < notas.txt

for op in Max Min
do
    pfx="$op: "
    declare -n oparr="alumne${op}"
    declare -n opval="Nota${op}"

    for alumne in "${oparr[@]}"
    do
        printf "%s%s %s" "$pfx" "$alumne" "$opval"
        pfx=", "
    done
    echo ""
done

Both of these generate:

Max: marta 70, luis 70
Min: pepe 5, ana 5