Can iOs app on iPhone have 2 Teslas?

Yes if they're within the same account. Tesla hasn't made it so that they can control multiple accounts in the app.

I tried getting Allen (remote S programmer) to add multiple account support but he said no

Yes, it can...

it must be added under the same user name. So if your MyTesla account for your cars are separate, it won't work, they must both exist in the same MyTesla account IIRC. What I do, is control one using the Tesla app, and other using the Model S app that Allen created.