We beseech Allah's (swt) all-encompassing mercy and forgiveness, and we invoke Him to make us amongst the sincere servants of Imam Al-Mahdi

.
The fourteen infallible figures, who are the Prophet

, Fatimatul Zahra

and the twelve Imams

, have achieved the highest level of perfection and infalliblity. However, this does not mean that other great individuals are not or cannot be infallible. The Ahlul Bayt

school of thought teaches that all of Allah's prophets are infallible without any doubt. The difference is that there are varying levels of infallibility, just as there are levels of sincerity. While the prophets sometimes may not heed the optional advice of Allah (swt), which is not mandatory (such as the action of Prophet Adam

eating from the tree), the fourteen infallibles obey Allah (swt) in every aspect. This is only one difference.
As for Abbas

and Assayeda Zaynab

, our scholars have established that they never committed a single sin (that deserves punishment on the Day of Judgment) in their lives. Although we have no specific
hadeeth that states they are "infallible" using the word "Ma'soom," our scholars conclude from the different Ziyaras (visitations) that they are infallible, but at a lower degree. These visitations speak so highly of both of them to the extent that they indicate they are infallible.
It is absolutely possible for a believer to live his/her entire life without sinning, but no one will ever reach the status of the fourteen infallibles

. Their infallibility represents the epitome of perfection and obedience.
Wassalam.
M. Baqer Al-Qazwini