I’m less clear about compatibility intervals right now but contrast() will provide the contrasts you seek, e.g., contrast(fit, list(group=1, bmi=25, age=30), list(group=2, bmi=25, age=30).
The trick with ExProb is that you have to see which arguments it creates in the generated function, and if the first argument is not the linear predictor, you need to create a little wrapper function that transfers its first argument to the appropriate one in the generated function.