The amendment in section 44AD as it pertains to partnership firm is to be understood in proper context. There is no disallowance sort of thing of remuneration. What is prescribed is that firm will not get a separate deduction of remuneration and interest on capital to partners out of net profit which is minimum 8% of gross turnover. In other words the minimum 8% net profit declared by the firm will include deduction of remuneration and interest on capital also. So thre is no disallownace of this expenditure.
As for double taxation, there is no double taxation at all since in the first place there is no disallowance in the hands of the firm and the same is taxable only in the hands of partners as was the case before also.