Are all the Popes saints?
If by saint you mean someone who is in heaven, well we have no idea if every Pope is in heaven or not. They could all be in heaven, but they might not all be. The only Popes we know for sure are in heaven are the ones that the Church has officially declared to be saints. The others may or may not be in heaven.
We should remember that Papal Infallibility only means that the Holy Spirit will protect official teachings of faith and morals issued by the Pope. Papal Infallibility does not mean the Pope is sinless. Popes suffer from original sin just like the rest of us and some responded to God’s grace better than others, just like the rest of us.