Myself and 2 siblings inherited a house and we all rec'd 1099s for 1/3 of the proceeds. Do I enter the full basis amount or 1/3 basis amount? Thanks!

If you each got a 1099 for 1/3 of the sale, then you would each use 1/3 of the basis as the purchase price.

Keep in mind that inheritance is not taxed.

If you inherit a house and then its sold, its possible (although not likely) that you may have some gain.