If you're referring to Formulaire d'Engagement, section 2 does not have any parts - it's simply identification of the principal applicant. Section 3 has a part B that is for les membres de la famille qui ne l'accompagnent pas au Quebec.
The sponsor would not be listed in that part, nor part A. The sponsor is not accompanying or non-accompanying - the sponsor is obviously a Quebec resident and Canadian PR or citizen. I'm going to assume you are the one sponsoring your wife. The principal applicant (that is, your wife, if she is being sponsored by you) needs to write those members of her nuclear family, basically, that will not be accompanying her to Quebec, and the associated details for each. I'm not sure what "signature part" you're referring to but for the last page of the Formulaire that I'm describing, the sponsor signs (once).
