There are numerous directories of railway stations in India. They do not all agree.
Some will list the first station (in an alphabetical list) as AB Junction near Agra Cantt. But it is a cabin and not a station.
The first station in the list is Abada (near Howrah on the way to Kharagpur):
Then there is this place on the Bengaluru-Hassan section on the SWR:
In some sources it is listed as Aadi….. so that would make it the first in the alphabetical list. Of course, there are many cases where the name on the station sign differs from the name listed in timetables or elsewhere.
The last entry is more clear-cut:
This is on the Suratgarh-Shri Ganganagar section in Rajasthan, on the NWR.
Coming to junction stations.
The first one is Abhanpur, near Raipur in Chhattisgarh. It was a narrow-gauge junction which is presently closed for conversion
So the first junction (which is presently functioning) is Abohar in Punjab:
No dispute about the last junction, Zafarabad near Jaunpur in eastern UP: