Driving Constant Current Through 2 LEDs from 2 Batteries
Think about a Joule Thief style boost converter running off a single AA battery. 

I gather you spec AAAA batteries because you have limited space yet believe battery voltage must exceed LED voltage. That's not true, says the Joule Thief.  

Customers hate oddball batteries.  We like normal battery sizes like AA, which have much more capacity while being cheaper than AAA or AAAA.   AAAA is rare and nobody will buy a product that uses them. 

Customers also hate devices that don't work with NiCD or NiMH rechargeable batteries (which output 1.2 volts per cell). 

More than one battery also means more than four contact surfaces to get dirty and corrode.  You know those horrible LED flashlights that are everywhere? They take 3 AAA's in a "cartridge" that's about the size (but not quite) of an 18650. 4 surfaces per battery, 4 for the cartridge, 2 for the bottom cap, and 2 for the switch.  No wonder they never work!  Into the trash it goes.  

It all says a boost converter off a single battery is the way to go.