Nobody knew about the Basilisk.
The only ghost or portrait who knew anything about the Basilisk and/or the opening of the Chamber was Myrtle. Harry didn't think to ask her until it occurred to him that her death was somehow connected to the Chamber, and this only happened towards the end of the year. Even when he did get around to asking Myrtle, her answer wasn't exactly all that descriptive.
"What do you want this time?"
"To ask you how you died," said Harry.
"No idea," said Myrtle in hushed tones. "I just remember seeing a pair of great big yellow eyes. My whole body sort of seized up, and then I was floating away..."
(Chamber of Secrets, Chapter 16, The Chamber of Secrets).
Myrtle didn't even know that it was a Basilisk which killed her, and she was the only ghost who had direct contact with it. She just thought that she'd died as a result of seeing yellow eyes. Harry already knew about the Basilisk at this point but if he hadn't have done then he (or Dumbledore) would've been none the wiser.
As for the other ghosts and the portraits, they didn't know any more than the students of the time. All they knew was the version of events as told by Riddle, which - after Hagrid's expulsion - became the official version of events.
In my fifth year, the Chamber was opened and the monster attacked several students, finally killing one. I caught the person who'd opened the Chamber and he was expelled. But the Headmaster, Professor Dippet, ashamed that such a thing had happened at Hogwarts, forbade me to tell the truth. A story was given out that the girl had died in a freak accident. They gave me a nice, shiny, engraved trophy for my trouble and warned me to keep my mouth shut.
(Chamber of Secrets, Chapter 13, The Very Secret Diary).
Since the truth was suppressed no-one had any means of knowing what actually happened.
The ghosts and portraits may have been around when the Chamber was first opened. But so was Dumbledore, and even he didn't know where the Chamber was or what the monster of legend was.
"The question is not who," said Dumbledore, his eyes on Colin. "The question is, how..."
(Chamber of Secrets, Chapter 10, The Rogue Bludger).
Can portraits be petrified?
No idea. It never happens so we have no means of telling. Ghosts can be petrified, though, so I suppose it's reasonable to suppose that other non-material personas can be too.