RDP from one AWS ec2 to other and ping from one ec2 to other

Question

I have two ec2 windows 2019 instances. Both are in same private subnet subnet and same security group. The security group allows all traffic for vpc cidr.

1. How to RDP from one private ec2(instance1) to another ec2 (instance2). When I try to rdp using privateip or private dns of instance1 to instance2, it does not allow me to change the username, and username appears as HOSTNAME1/Administrator.

2. I am not able to ping one ec2 from other. however both are in same subnet and same security group and allows all traffic within VPC CIDR