Theory:

     Usha’s heart was in her mouth. She had seen, without a shadow of a doubt, two ghostly creatures at the other side of the room, and she wasn’t going to remain in that ruined building a minute longer.

     She ran out of her corner, ran towards the big gap in the wall through which she had entered. She was halfway across the open space when something – someone – fell against her. She stumbled, got up and again bumped into something. She gave a frightened scream. Someone else screamed. And then there was a shout, a boy’s shout, and Usha instantly recognized the voice.
 
‘Suresh!’

     ‘Usha!’

‘Binya!’

     ‘It’s me!’

‘It’s us!’
Explanation:
 
Usha was very frightened now, she was sure she saw two shadows, and they looked like ghosts. She just wanted to run away from that place.
 
She tried to venture out from the place from where she had entered, the big gap between the wall. When she was just halfway, something fell on her. She got up but stumbled again on something. She screamed, but there was someone else also who cried along with her. And then there was a shout, Usha recognized that voice, she was sure of that.
 
She called out to her brother, "Suresh!"
 
Then came a reply, "Usha!"
 
Usha called out again, "Binya!"
 
It's me, Usha here.
 
And the reply was, "It is us" Binya and Suresh.
 
Meanings of difficult words:
 
Numbers
Word
Meanings
1.
Creatures
Animals, or beasts.
2.
StumbledTripped.
3.
Instantly Immediately.
Reference:
State Council of Educational Research and Training (2019). Term-1 English Standard-7. The Wind on Haunted Hill by Ruskin Bond  (pp. 25-34). Published by the Tamil Nadu Textbook and Educational Services Corporation.