Why do you need 2 USB for Tails?
You can also use two USBs to install and run Tails. Using two USBs is to use the Tail installer for incremental updates and create a secure encrypted persistent storage. You can use just one USB drive if you do not need encrypted storage. For this, you need two USB drives of at least 4GB of storage each.
Can I install Tails on a memory card?
This is not possible using the recommended installation methods. Tails is designed to be a live system running from a removable media: USB stick or DVD.