You could cheat.. and when ever Sammy asks out.. you take Kirby with you.

but right now,, since Kirby is so new at your place.. i woudlnt allow him to use the doggy door even if you had one. he needs lots more time to adjust to you,, the house,, your yard.. and even his fuzhead brother. thats a lot for any dog to get used too in a very shor time. i know it seems like hes settled right in,, but he still needs time to create a bond with you yet. it does take a little time. hes probably not even really used to the house yet even.

wish i could be more of help.
but i wish you and your two fuznuggets the best of luck.