If your sisters include your house property acquired by you through said WILL, you can file application for objection for the same and file suitable WS seperately.
WILL registered or non registered have equal value, hence you need not get your self disturbed for the same.
If the said house was self acquired property of your mother, then she had every right to prepare WILL for the same, hence you need not worry. But, if it happened to be parental property, then you can be in troble becauase your mother did not have right to execute WILL.
For appropriate advice complete details are required.