Grammar, Usage / That vs Which - what is proper usage? [9]

Need clarification on using which or what??

hi,
can i use which with multiple answers?

Ex:

which are your pens among these?
or should it be :
what are your pens among these?

also

which tow children are yours among those students?
or
who are your children (two) among those students?

thanks

Grammar, Usage / That vs Which - what is proper usage? [9]

thanks

but for the first one>>>

the answer is going to be "my pens are the red and the blue"

it means that the questioner knows that the answer has more than 1 choice

so can it be "which two pens are yours among these?"
or should we use "what two pens are yours among these?"