You would need to make sure that your parents send the bitcoins from an address they control, so that they can sign a private message with and they can prove that it really were them who sent the coins. You would need to receive the coins in your own wallet too, then send it to your exchange, turn them to fiat and withdraw to your bank account.

At the end it would be provable that these funds were sent from your parents. You can't be charged for something you received from your parents since it's not something you earned by working for it.

If we in germany get money from someone we know and it is not a reward for a work then it is tax free of course. I'm only not fully sure if the transfer over a border can change anything. The one year holding time is of no matter to you at all at least.

That's only my opinion on the matter though. Maybe someone other has a different opinion.

Ask a pro but you're just using it as a remittance service. Western Union isn't taxed in that way so I don't see why this should either. The German one year rule applies to capital gains taxes. As I assume you'll be converting them nearly instantly there won't be any capital gains.