You might consider using Go To related records instead of performing a find, but the scripted find is working OK. You might also consider searching for an ID number from the Au Pair table as you might get two candidates with the same name and then your current method will fail at times to find the correct Au Pair record.
Your email pulls the first address because changing layouts loses the focus on the portal row clicked to start performing this script. What you can do is set a variable to the email as the second line of this script and then your send mail script step can refer to the variable for the email address instead of the email field. This can also be done for any other information you might need from the Au Pair table such as a name or phone number.
I don't know why I was making it so complicated by going through the portal.... The solution is much easier....
1) At the top of the script, stored the Family and Au Pair ID's in a global Variable
2) Created a layout for the Interview table
3) Go to the layout and perform a find on both ID's
And that's it!
btw, thanks for the thing about searching on Au Pair name to Au Pair ID - I changed that too.