Lets assume we have transaction with 2 inputs, each worth 1 bitcoin, and we send these 2 bitcoins to one address.
- What happens if there is successful double spend attack on bitcoins in our first input?
- How many bitcoins recipient gets, one or zero?
A transaction either gets confirmed in its entirety (by being included in a block) or none at all. If one of the inputs is successfully doublespent, then your tx is invalid so will never be confirmed.