Do microwaves sterilise feeding bottles in the steamer given to use in them. If so how to sterilise the bottles?

The best way to sterilize bottles is to steam them for a few minutes in a large pot on the stove with a little water. They can also be sterilized in an industrial dishwasher with a "sterilize" function.

Microwaves are non-ionizing radiation. They do not sterilize anything by themselves, except to the extent that they can boil water. It would be possible to sterilize bottles in a microwave, assuming that you had a microwave-safe container that you could boil water and bottles in. (Never put a sealed container in a microwave).