In his book “Sharhul ziyaratul jamiatul Kabira” Abdullah Shubbar said:

هم عليهم السلام أفضل الانبياء والمرسلين ما عدا جدهم خاتم النبيين

They (alaihuma salam) better than prophets and messengers except their grandfather, the seal of prophets.

Source: Aytollat Shubbar, “Sharhul ziyaratul jamiatul kabira” p 63.

And he said at the page 74:

فانهم حجج الله تعالى بل أعلاهم وهم المتصفون بصفات الله تعالى فكأنهم صفاته بل هم مظاهر أسمائه وصفاته

They are hujjas (proofs) of Allah Taala, nay most exalted ones, and they described by characteristics  (sifaats) of Allah, as if they are His attributes, nay they manifestations of His names and Attributes.