How can I incorporate brown lettuce into something appetizing?
Brown lettuce may or may not be harmful to you, it depends on how far gone it is. 

We get a lot of questions on this forum asking about how to use ingredients which may be past their prime, and the advice is almost always not to try - mixing bad ingredients with good ingredients is almost always going to ruin your good ingredients and waste time and money. 

So don't try to incorporate it into anything, either make a dish that can stand on its own or throw it away. If it's not smelly, or slimy, or looks rotting then taste it. Try each type of leaf in each bag, if they taste ok then you could try making something out of it. 

Personally I'd chuck it. I wouldn't want to be served brown lettuce, and I wouldn't serve it to anyone else.