Every man his own currency you may think in these modern times...and even more confused when sites like XAPO offers collective Wallets and sites like BitMixer offers a Wallet of mixed currencys.
Can someone please explain how to act with theese to be on the safe side?
You are getting these points wrong.
Xapo is a Switzerland-based company that provides a bitcoin wallet combined with a cold storage vault and a bitcoin-based debit card. (from Wikipedia) and Bitmixer is a mixing service wherein you mix your coins in different wallets so as to conceal any traces of you and where the bitcoins will be after the mixing process. To simply explain this, Xapo is a wallet provider and Bitmixer is a service to help you cover the traces of your spending.