Which coins offer a 2 factor authentication feature built into the blockchain without a centralize authority? Which coins have the ability to offer a 2 factor authentication feature where it requires a secondary approval mechanism in order to spend from an address?
Have a look at byteball (http://byteball.org). It supports n-of-m wallets out of the box which can be used to implement a basic 2FA mechanism (2-of-2 with your desktop and your smartphone, for example.)

It also has a chat mechanism built in, which can be used to communicate between the devices and which would probably enable you to do what you intend.

There are a number of other interesting features listed at the web site.