Hi,
I think this can be achieved with standard only.
After maintain Punch as you said, check TIP entry. Standard function will 15 mins gap in some time type if its configured accordingly.
Or else you can write PCR to calculate the difference. (Let me know if PCR required, We will guide you).
For specific group, make PCR grouping separately for these two employee subgroup.
Let me know if further help required.
Thanks,
Ketul