Oh my all those poor recent popes, P6, JP2, B16, and Francis who have committed mortal sins by participating in inter-denominational worship services. B16 and Francis still have a chance to repent and avoid going to hell because of their mortal sin, but it would sure seem that P6 and JP2 are beyond redemption. Not only did they pray together with non-Catholics, but they did so publicly. Since such public sin requires public confession to expurgate, and they never did express sincere sorry for their public sin, we would appear to have no choice but to conclude that they died in their sin.

To die in mortal sin is to be condemned to hell.

Now all that is clear enough.

What concerns me is the fact that the same infallible Church that established these actions as mortal sins also declared the JP2 to be a Saint, which mean he is absolutely known to be in heaven. But how can JP2 both be simultaneously in heaven and hell?

Can you help me out here, mjmchal; since you know the rules.