Install them this way?

nixos/shared/scripts/dvd.nix

@@ -0,0 +1,17 @@
+{
+  lib,
+  stdenv,
+  direnv,
+  writeShellApplication,
+}:
+writeShellApplication
+{
+  name = "dvd";
+
+  runtimeInputs = [echo direnv];
+
+  text = ''
+    echo "use flake \"github:the-nix-way/dev-templates?dir=$1\"" >> .envrc
+    direnv allow
+  '';
+}

nixos/shared/scripts/dvt.nix

@@ -0,0 +1,17 @@
+{
+  lib,
+  stdenv,
+  direnv,
+  writeShellApplication,
+}:
+writeShellApplication
+{
+  name = "dvt";
+
+  runtimeInputs = [direnv nix];
+
+  text = ''
+    nix flake init -t "github:the-nix-way/dev-templates#$1"
+    direnv allow
+  '';
+}