First, congrats on having that family heirloom. Shootable or not it is great you have it.
Can't tell much about the rifling, hopefully it still has some.
First, do derust the barrel inside. Evaporust and steel wool should clean it up.
Do have it checked by a competent muzzle loading gunsmith. Failing that, just examine yourself very closely. Pull the nipple and replace.
Load very lightly, shoot and examine for any leaks at the breech and lug/sight dovetails.
If safe, start shooting, work up a hunting load and go hunting. The report back here on results.