Is this a sequel to The Uninvited?

No. This was actually filmed four years ago. It just took a while to get it finished.

Yes. And the sequel to this sequel was titled 'The Ones Who RSVP'd, But Didn't Show Up'. That one stars Ritchie Valens' corpse, and was such a hit in advance screenings that the decision was made to release it straight to Betamax last year. Check the bin at Walmart where they pay you $5 to take it.