Catholics recognize that the Orthodox have apostolic succession. Except for some Anglicans and maybe some Lutherans, not sure any other Christian group has the same understanding as Orthodox/Catholics with apostolic succession.
As far as being destined for hell, Pope Benedict confirmed this:
“It follows that these separated churches and Communities, though we believe they suffer from defects, are deprived neither of significance nor importance in the mystery of salvation. In fact the Spirit of Christ has not refrained from using them as instruments of salvation, whose value derives from that fullness of grace and of truth which has been entrusted to the Catholic Church”
So if your Catholic friends disagree tell them to take it up with the Pope.
Freegards
Thanks to everyone who responded. I might let someone at our church whose mother was Catholic and father Protestant know that the nun at her school who told her that her father was going to Hell was in error. She knows that now but it was more than a little traumatic for a little girl to hear.