What's wrong with being a solo founder? Was there any guideline that said you have to have a 2-3 co-founders?
In our case, the other founder is very much a part of this company but we didn't have to transfer 10% equity and that never a concern with any of us. We are in prototyping stage and equity distribution right now was not our top concern.
So only one founder filled the Founder's Form and everyone was there in the video.
I didn't know YC S18 had a rule of "No SOLO founders".
And that they won't even check our application properly because of that.