multiple projects per EC2 with Load Balancers
You can archive that, but you will need to use the Application Load Balancer (ALB) which allows you to create rules (like HTTP URL paths, host header conditionals, query strings, HTTP method) to forward the traffic to a specific pool of servers that on your case would be those 2 EC2 instances. 

e.g.:

/app1 --> :/app1
/app2 --> :/app2

Notice that you should have the ALB rule like this: /app1/* and /app2/*