Are you not able to do it by defining new fields in the inherited model like this

class A(models.Model):

field1

field2

class B(models.Model):

_inherit="A"

one2many_field = fields.One2many(codmodel, inverse_name)

many2many_field = fields.Many2many(comodel)

??

Would have been nicer if you could add more information about the problem you're facing.

@Karan BK, hey there I've found the solution. What I have done wrong is not mentioned inverse relation in my main module, after doing this things works well, anyway thanks for response. Thanks