1) Should you go out of your way to avoid telling someone that you preform salatul layl? E.g. of someone asks me do i have to try and defer the question
2) Can I pray my qadha salah as part of salatul layl?

1) Depends on your intention – if it’s to encourage the other person to also pray it is good
2) You can pray the two rakat salaahs in Tahajjud as ma fi dhimma and thus would count as qatha if you have any