can an irule call another irule

Can you write the iRule so as it is general enough to be used for both virtuals?

If not, try using procs. See this link:

Getting Started with iRules Procedures

There is an example about calling code that is outside the current iRule.

is it available in v10.x?

no, it is introduced in 11.4.0.

Getting Started with iRules Procedures by Jason Rahm

If I may add, procs would definitely be the way to go here. I might have also said that a sideband call might work, but that too requires v11. There still may be a way though, depending on how the main rule interacts with the VIPs, and at what (if any) event level it needs to fire. So lets say for example you have a main rule that gets triggered at HTTP_REQUEST, and your two almost identical iRules, which probably also trigger code at HTTP_REQUEST. You could add the main rule to each VIP and use a few conditions inside that iRule to determine when and what to run. For example:

VIP iRule:

when HTTP_REQUEST {
    ...doing something important here
}  

Main iRule:

when HTTP_REQUEST priority 501 {
    switch [virtual] {
        "app1-vs" {
             do something for app1
        }
        "app2-vs" {
             do something for app2
        }
    }
}

In this way, you have a single main iRule that 1) gets triggered after your VIP-specific iRule, and 2) evaluates code based on the caller VIP.