If you have rounded off oil drain plug the best solution would be to buy a replacement plug with washer first.

Removal may be possible with a very tight grip from a set of molegrips to slacken off then carefully  take out with waterpipe pliers to avoid stressing the sump.

Fuel filter can be fiddly and is far easier with purpose made pliers.At each end of the filter is a small plastic clip which requires both small tangs compressing and then pulling off the pipe.Not too hard with 2 small screw drivers to press down but you then need a 3rd hand to pull off the pipe.If you have bought a new fuel filter worth buying the 2 small clips incase the existing ones get damaged..only a few pence and better to be safe.

You can get from places like Machine Mart sockets that removed Rounded Bolt Heads. They tighten on the Bolt Head whilst undoing
Hope that makes sense but they are brillant