I only learned Gittin briefly. however, i’m pretty sure that if there are 2 slichim, they don’t have to say befanai nictav at all. The Reason for the statement to begin with is that there is one shaliach. Therefore, as someone said above, we apply “meidak diak” and “ikiloo bah rbanan mishum aguna” and finally the statement of befanai nectav and vioala… one shaliach is believed like 2 would be. however, if you have 2 people delivering, i believe the statement is irrelevant anyways. unless you wanna argue that the statement is actually megaraayiah their testimony. that’s possible. what they would do in such a case is just ask the shlichim to say hikarti (i recognize the signature) and that would make the get kayam. (all of the above is according to rava (with an aleph) and may not be true for Rabba. Rabba holds they would have to say befanai i think) (Rabba learns the mishnah that they have to say befanai when they are 2 shlichim “davka”. rava says lav davka )