I have two ERC20 tokens that I created on Ethereum. I would like to know if it is possible for me to create a mobile application that will allow my users to check their balance (for tokens) and transfer them tokens, a kind of wallet app, if possible with multisig functionality...
Sure it's possible. A very basic wallet is simply an interface to the blockchain. On top of that you can add multiple features (such as multisig, sending transactions, ...)
What you need is:
1) Code for the wallet
2) A node to connect to to get access to the blockchain
However I don't recommend writing a wallet by yourself as it's very risky and easy to make mistakes. Such mistakes may cause you and your customers to lose all their assets somewhere in the future. If you google you can probably find existing open source wallets for almost any language you prefer - also mobile.