The situation is described in the following diagram:

$($this is the way it is configured$).$

The Route Tables and the Security Group are in the diagram.

$($Note: the NACLs allow All traffic inbound and outbound$)$

What can the two EC$2$ instances reach?

Question $3$ options:

The EC$2$ instances can SSH each other but they have no Internet access

The EC$2$ instances can only reach other EC$2$s attached to their respective subnets.

The EC$2$ instances can be reached from the Internet only.

The EC$2$ instances can be reached from the Internet via SSH plus they can reach each other with SSH also.