Brew install fails on some packages

[alistairstead]

==> Satisfying dependencies
==> Downloading https://dl.google.com/chrome/mac/stable/GGRO/googlechrome.dmg
==> Verifying SHA-256 checksum for Cask 'google-chrome'.
==> Installing Cask google-chrome
Error: It seems there is already an App at '/Applications/Google Chrome.app'.
==> Purging files for version 71.0.3578.98 of Cask google-chrome
Installing google-chrome has failed!
Installing google-chrome-canary
Installing google-cloud-sdk
Installing grammarly
Installing gyazo
Installing imagealpha
Installing imageoptim
Installing iterm2
Installing kaleidoscope
Password:
Installing java
Installing java8
Installing kap
Installing keybase
Installing postman
Installing rocket
Installing skyfonts
Installing skype
==> Satisfying dependencies
==> Downloading https://downloads.slack-edge.com/mac_releases/Slack-3.3.3-macOS.zip
==> Verifying SHA-256 checksum for Cask 'slack'.
==> Installing Cask slack
Error: It seems there is already an App at '/Applications/Slack.app'.
==> Purging files for version 3.3.3 of Cask slack
Installing slack has failed!
Password:
Installing teamviewer
Installing transmit
Installing transmission
==> Satisfying dependencies
==> Downloading https://dl.devmate.com/com.macpaw.site.theunarchiver/120/1528909123/TheUnarchiver-120.zip
==> Verifying SHA-256 checksum for Cask 'the-unarchiver'.
==> Installing Cask the-unarchiver
Error: It seems there is already an App at '/Applications/The Unarchiver.app'.
==> Purging files for version 4.0.0,120:1528909123 of Cask the-unarchiver
Installing the-unarchiver has failed!
Installing tunnelbear
==> Caveats
To install and/or use virtualbox you may need to enable their kernel extension in

  System Preferences → Security & Privacy → General

For more information refer to vendor documentation or the Apple Technical Note:

  https://developer.apple.com/library/content/technotes/tn2459/_index.html

==> Satisfying dependencies
==> Downloading https://download.virtualbox.org/virtualbox/6.0.0/VirtualBox-6.0.0-127566-OSX.dmg
==> Verifying SHA-256 checksum for Cask 'virtualbox'.
==> Installing Cask virtualbox
==> Running installer for virtualbox; your password may be necessary.
==> Package installers may write to any location; options such as --appdir are ignored.
Error: Failure while executing; `/usr/bin/sudo -E -- env LOGNAME=alistairstead USER=alistairstead USERNAME=alistairstead /usr/sbin/installer -pkg /usr/local/Caskroom/virtualbox/6.0.0,127566/VirtualBox.pkg -target /` exited with 1. Here's the output:
installer: Package name is Oracle VM VirtualBox
installer: Installing at base path /
installer: The install failed (The Installer encountered an error that caused the installation to fail. Contact the software manufacturer for assistance.)

Follow the instructions here:
  https://github.com/Homebrew/homebrew-cask#reporting-bugs
/usr/local/Homebrew/Library/Homebrew/system_command.rb:107:in `assert_success'
/usr/local/Homebrew/Library/Homebrew/system_command.rb:50:in `run!'
/usr/local/Homebrew/Library/Homebrew/system_command.rb:27:in `run'
/usr/local/Homebrew/Library/Homebrew/system_command.rb:31:in `run!'
/usr/local/Homebrew/Library/Homebrew/cask/artifact/pkg.rb:59:in `block in run_installer'
/usr/local/Homebrew/Library/Homebrew/cask/artifact/pkg.rb:65:in `with_choices_file'
/usr/local/Homebrew/Library/Homebrew/cask/artifact/pkg.rb:52:in `run_installer'
/usr/local/Homebrew/Library/Homebrew/cask/artifact/pkg.rb:32:in `install_phase'
/usr/local/Homebrew/Library/Homebrew/cask/installer.rb:209:in `block in install_artifacts'
/System/Library/Frameworks/Ruby.framework/Versions/2.3/usr/lib/ruby/2.3.0/set.rb:674:in `each'
/System/Library/Frameworks/Ruby.framework/Versions/2.3/usr/lib/ruby/2.3.0/set.rb:674:in `each'
/usr/local/Homebrew/Library/Homebrew/cask/installer.rb:200:in `install_artifacts'
/usr/local/Homebrew/Library/Homebrew/cask/installer.rb:95:in `install'
/usr/local/Homebrew/Library/Homebrew/cask/cmd/install.rb:21:in `block in run'
/usr/local/Homebrew/Library/Homebrew/cask/cmd/install.rb:14:in `each'
/usr/local/Homebrew/Library/Homebrew/cask/cmd/install.rb:14:in `run'
/usr/local/Homebrew/Library/Homebrew/cask/cmd/abstract_command.rb:34:in `run'
/usr/local/Homebrew/Library/Homebrew/cask/cmd.rb:89:in `run_command'
/usr/local/Homebrew/Library/Homebrew/cask/cmd.rb:155:in `run'
/usr/local/Homebrew/Library/Homebrew/cask/cmd.rb:120:in `run'
/usr/local/Homebrew/Library/Homebrew/cmd/cask.rb:7:in `cask'
/usr/local/Homebrew/Library/Homebrew/brew.rb:89:in `<main>'
installer: Package name is Oracle VM VirtualBox
installer: Installing at base path /
installer: The install failed (The Installer encountered an error that caused the installation to fail. Contact the software manufacturer for assistance.)
==> Purging files for version 6.0.0,127566 of Cask virtualbox
Installing virtualbox has failed!
Installing vlc
Installing qlcolorcode
Error: Cask 'qlimagesize' is unavailable: No Cask with this name exists.
Installing qlimagesize has failed!
Installing qlmarkdown
Installing qlprettypatch
Installing qlstephen
Installing quicklook-csv
Installing quicklook-json
Installing suspicious-package
Installing webpquicklook
Password:
Installing qlvideo
Installing caskroom/fonts/font-anonymouspro-nerd-font-mono
Installing caskroom/fonts/font-awesome-terminal-fonts
Installing caskroom/fonts/font-fira-code
Installing caskroom/fonts/font-symbola
Installing caskroom/fonts/font-fontawesome
Installing caskroom/fonts/font-material-icons
Homebrew Bundle failed! 5 Brewfile dependencies failed to install.