You can try to emulate HT12D with PIC16F84a itself (if you still have free space and ports for that).

Recently, I had a similar problem and decided to create an emulator for HT12D with PIC12F675. In my project, I used an HT12D and a CD4093 for a flood alarm system. Both have been replaced by a unique PIC12F675 (drastically reducing the bill of materials).

My emulator project for HT12D using PIC is available on github (HT12D_PIC_Emulator).

Important notice: This project was entirely created by me and is completely free. I'm not trying to self-promote, I'm just trying to help.