Personally I would close. If you let parents have the option of coming, with so many of your own family members feeling ill, I think it will just keep getting spread back and forth and I would want to nip it in the bud and be done.
I would close, have everyone get some much needed rest and I would also sanitize the heck out of the house so you are all bright eyed and bushy tailed for Thursday.
I am sure your parents don't necessarily want their kids to be exposed any more than necessary.
Hoping everyone in your house feels better soon.
