Question
the bark is looking loose & small ferns are growing on some limbs is this tree sick?

Answer
As long as the foliage is green and healthy looking the tree is ok. Ferns do grow on some older oaks and the bark can sluff off these older oaks. All this is normal and if the foliage is ok the tree is fine. If a tree is having problems it will show up in dieback of foliage. Sounds like your tree is fine.