In your case, before purchasing the shares by ‘A’ limited, you should be complied with the SEBI – (Substantial Acquisition of Shares and Takeovers) Regulations, 1997.
Further, the promoter of “B’ limited is an individual, the following categories are fall in purview of definition of Promoter and Promoter group under said regulation.
(i) His spouse, parents, brothers, sisters and children;
(ii) Any company in which 26% or more of the equity share capital is held by him or by the persons mentioned in sub clause(i) is a partner or member;
(iii) Any company in which a company specified in sub-clause(ii), holds more than 50% of the equity share capital;
(iv) Any firm in which the aggregate of his holding and the holdings of persons mentioned in sub-clause (i) is more than 50% percent.
Certain disclosures need to be made depend upon the quantity shares or voting rights acquired by ‘A’ Limited.
After Purchasing, the shares ceiling limit of promoter or promoters group shall not exceed the limit as prescribed by SEBI or As per Listing Agreement.