AlterBrains

Can we do this with mighhtysites

Main site is sub1.domain1.com ( Sub Domain)

Slave site 1 : domain2.com ( parked domain) -- duplicate site with different template
Slave site 2 : sub2.domain2.com ( parked domain) -- -- duplicate site with different template

All are in same cpanel
domain1.com is pointing to /
sub1.domain1.com is pointing to /sub1

Please send me the manual.

I think that's possible, but please also ask your hosting provider if these domains will work.
Not really sure if cPanel allows to setup a parked domain for subdomain.

I want to have m.domain1.com and tab.domain1.com for domain1.com to have mobile and tablet versions so domain1.com is master and m.domain1.com and tab.domain1.com are slaves. can I do that?

Yes, you can setup parked domains m.domain1.com and tab.domain1 for domain1.com, so all 3 sites will use same files.