Shimano Hollowtech left crank arm getting loose
Thread lock will help hold the bolts on. I would apply it to the bolt thread, and not the actual crank arm thread. You will need more force to remove them when you do come to remove the crankset. But they shouldn't need any more strength to put them on. Just tighten them to the recommended torque setting (it should have it written on the crank arm).

Fundamentally though, it sounds like you have a few problems which only a new crankset and BB would solve.

I got a Tiagra Hollowtech chainset on ebay for around £30-£40. It might cause more harm than good trying to threadlock it all together, and give you more problems when trying to get it off and replace it later down the line.