You can easily update your own package, without updating stable packages. Indeed, Composer allows the wildcard * with the update command. Imagine that your packages are prefixed by acme (acme/cache, acme/awesome-component, ...), you should execute this command :
composer update "acme*"
If you have packages without the same prefix, no worry, just execute this command :
composer update "acme*" "other-prefix*" "yet-another-prefix*"
So, when you run a composer install, don't forget to run the composer update "prefix*" command after to update your own shared packages because the composer.lock keeps only the installation commit reference (after the first composer install command), and not your branches HEAD.
See Disable this plugin in development environment (for CI purpose, for example).