I'd maybe set up an intercut as with phone conversations, and make each computer monitor different so that when we see it we'll know right away whose it it, e.g.
INT. BOB'S BEDROOM - NIGHT
BOB, a nerdy 17-year-old, types frantically at his computer. His display is a 21" stealth black LCD.
BOB'S DISPLAY - "Welcome to the Sizzling Hot Dates chatroom, please sign in."
Bob types--
BOB'S DISPLAY - "sweetbuns is logged in."
INT. SHIRLEY'S BEDROOM - NIGHT
SHIRLEY, 85, sits in a grubby dressing gown, wreathed in cigarette smoke. She reads her display and grins toothlessly. Her ancient display has plastic flowers and furry creatures stuck along the top. The screen is greasy, some of the characters are blurred. She types--
INTERCUT
BOB'S DISPLAY - "hotchick99: do you really have sweet buns?"
Bob grins. He types--
BOB'S DISPLAY - "you bet. r u really a hot chick?"
SHIRLEY'S DISPLAY - "sweetbuns: you bet. r u really a hot chick?"
Shirley claps her hand in delight. She types--
BOB'S DISPLAY - "hotchick99: honey I am so hot you would melt if I licked you"
Bob grins and types--
Shirley reads her display and grins. She types--
BOB'S DISPLAY - "hotchick99: let's go private and talk dirty"
Bob's eyes widen with interest.
etc.
-Derek
My wittle web page - hack stories, failed novels, dud screenplays, terminal writer's block.
Another one of them new worlds. No beer, no women, no pool parlors, nothin'. Nothin' to do but throw rocks at tin cans, and we gotta bring our own tin cans.