dear friends
BUYER SELLER QUANTITY OI VOL
A(new) B(new) 50 50 50
C(new) D(new) 30 80 80
E(new) F(new) 100 180 180
G(new) H(new) 30 210 210
I(new) A(old) 50 210 260
B(old) J(new) 30 210 290
D(old) E(old) 30 180 320

Short Cut
Take N as new participant(one who wants to take fresh position) and O as old participant(one who wants to square up position)

then N to N oi increase volume increase equally
N to O
or O to N remain oi constant but volume increase by traded
contract
O to O oi decrease and volume increase with same contract

every scenario volume increase but oi may increase , remain constant or decrease