I was speaking to a Shai brother who mentioned that the chain of narrators for dua tawassul and Nudba were weak and that Dua Kumayl is found in a book by Al Tusi without any chain so we have no way to authenticate it came from Imam Ali. If I understand correctly you are saying that this is incorrect and these are actually from authentic sources with a reliable chain?

Dua tawassul: not all that we recite are traceable from our traditions. Some part such as the first line regarding the tawassul of prophet are traceable in our traditions. Other part are not necessary traceable but we recite due to the fact that Imams are true and legitimate successors of the prophet and whatever is given to prophet goes to Imam by the fact of succession.

Dua Kumayl: The earliest and most reliable source that contains the chains for Dua Kumayl is Al-Saduq’s Kamal Al-Deen 1/274-279

From Abdullah bin Mohammad bin Abdullah bin Mohammad bin Abdulwahab bin Nasr bin Abdulwahab Al-Qurashi, from Abi Bakr Mohammad bin Dawud bin Sulaiman Al-Nisapuri, from Musa bin Ishaaq Al-Ansari the judge of Ray, from Abu Nu’aym Dhirar bin Surd Al-Taymi, from Asim bin Humaid Al-Hannat, from Abi Hamza, from Abdulrahman bin Jundub Al-Fazzari, from Kumayl bin Ziyad.

Dua Nudba:
It is an important and authentic Dua. It's deep meaning penetrates to the depths of the heart. This is enough proof that these are not the words of an ordinary person. They are uttered by the personality who has connection with the celestial world (Aalam-e-Malakoot). Allamah Muhammad Baqir Majlisi (r.a.) has quoted this Dua in 'Zaad-ul-Maad' from Imam Jafar-e-Sadiq (a.s.). It is for the Imam of the time. And Muhammad bin Ali bin Abi Khura has quoted this dua from the book of Muhammad bin Husain bin Sufyan Bazoofari, from Imam-e-Asr. Apart from this, great Shia scholar Sayed Raziuddin bin Tawoos has mentioned it in his book, "Iqbal" on page no.295 to 299. Muhammad bin Jafar Mashadi Haeri has recorded it in book Al-Mazaan (Dua no.107). Qutb Rawandi in Al-Mazaar also records it and so does Allamah Majlisi in 'Zaad-ul-Maad' and 'Beeharul Anwaar'. Shaykh Abbas Qummi too has narrated it in his book, 'Mafatihul Janan'.