1. A pro forma defendant is a defendant named as a matter of formality, who typically has no direct responsibility for the harm alleged, but shares an interest with other defendants, such as being a co-owner of property or successor in interest. For example, a co-owner named on a deed or an heir who inherits property may be named as a pro forma defendant. A pro forma defendant is a term used mainly in Indian law.A proforma defendant is a defendant against whom no relief is sought. He is arrayed as party only to avoid the defect of nonjoinder of parties.
So here when a1 and a2 surrendered as provided in the facts provided by you; they portrayed their bonafide intention and innocence. At the same time they showed the involvement of a3 i.e the involvement of the lady(a3) in the dacoity claiming that they have no direct responsibility for the harm alleged. But they just share an interest with other defendants. That is the reason why they are now considered/named as proforma defendant.
2. It has been the practice of the Supreme Court not to hear a special leave petition directed against an order of conviction and sentence, till the petitioner has surrendered. Rule 6 of Order XXI of the Supreme Court Rules requires that the petitioner must first surrender and produce the surrender certificate before the petition is heard. However, the petitioner can, if so advised, move an application for exemption from surrendering. In such a case, the application for exemption is listed before the Court for orders.However where the High Court has granted time to surrender and the petitioner has moved the Supreme Court by special leave within that period with an application for exemption from surrender, such petition, if fixed for admission before the date of the surrender allowed by the High Court, may be heard. IT ALL DEPENDS ON THE COURTS DISCRETION WHETHER OR NOT TO GRANT THE DECREE IN FAVOUR OF THE APPLICANT OR NOT BASED ON WHETHER THEY FIND THE GROUNDS OF APPEAL REASONABLE OR NOT.