Can I use multiple wallet apps (MetaMask, BitKeep, Walletconnect & Wombat) to play Planet IX?

Yes, but you must use different browsers or profiles in that browser. For example, if you have a MetaMask in Google Chrome, you can use the same seed phrase to set up a BitKeep in Brave Browser. However, if you attempt to use two wallet applications on the same profile the application that was first installed will be prioritised.