残る and 残す: leftover food and a saved portion
Distinguish an amount left over from a portion someone leaves, and examine staying in a place and leaving a record.
Check the amount remaining
パンが二つ残っています。 says that two pieces of bread remain. 残る, read のこる, makes the remaining item the subject without specifying whether someone saved it deliberately.
もう一つも残っていません。 means that not even one remains now. Read 一つも together with the negative rather than interpreting it as one item still being available.
Leave a portion for someone
弟のためにパンを一つ残しました。 says that the speaker left one piece of bread for their younger brother. 残す, read のこす, marks the saved item with を.
食べきれなくて、ご飯を少し残しました。 means that someone could not finish the rice and left some. 残す does not always imply deliberate saving for later.
Use it with places and records
忘れ物を探すため、教室に残りました。 says that the speaker stayed in the classroom to look for something left behind. 教室に is the location where the person stayed.
変更した理由をメモに残してください。 asks someone to leave a note recording the reason for the change. 理由を is the recorded content, and メモに indicates where it is recorded.
Does パンが二つ残っています establish that someone saved bread for a younger sibling?
Show the answer and why
No. It states only that two pieces of bread remain. The intended recipient and any intention to save them require additional explanation.