Jack the car up, take off the dustcap in the middle of the hub, take off the split pin, undo the 30mm nut which SHOULD be loose, it's normal and should be only nipped up (let the garage do it) the wheel will then come off with the brake drum. This will be an annoying job due to limited space but is more then doable.
Then take it to the garage and they can remove the bolts and inspect the drum. If the threads are gone in a drum, then you might as well just get a new pair of drums if it's the bolts then two new bolts.
Are they aftermarket wheels?
I also would just drive it but can't say I reccomend it (just incase something happens) but you'd be fine. I was driving around daily in a car which work bought and turns out it only had two out of 5 bolts in each front wheel.
