ANSWER:

What they are doing is wrong and against the sunnah!

These 2 Imams are repressing the imam of the masjid and not themselves. Therefore, when one of them offers witr, and the other one offers another witr as the end of tahajjud, this is as if the Imam offered two witr in the same night, disobeying the Prophet salla Allahu Alaihi wa sallam. 

For you, add another Rakah with the witr of taraweeh and then offer it at the end of tahajjud so that you would have only prayed one witr.

In ramdan last ten ,For tharaweeh our masjid the imam skip the witr and Prayed after thahajud . But the same time another imam lead witr after tharaweeh. So can I get full benefit of praying full night with the imam who skip witr after tharaweeh and and praying thahajud late night with witr.

Taraweeh, Tahajjud and Qiyam-ul-Layl | May 29, 2019 11:32 am
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I started new job, they only had a night shift, i will be working for roughly 80% of the night. It will be like this for 5 of the last 10 nights. Should i do my best to swap my shift with a person on a day shift such as giving them money to swap with me, or can i get the same benefit of 83+ yrs if i had sincere intention of worshipping the whole night, but my work stopped me?
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During taraweeh or tahajjud can the people in congregation behind the imam use the phone to read the translation of what the imam is reciting. For ex. If imam said he will recite surah ya seen in first raka and rahman in 2and. Can the congregation get their phones out and read the translation from quran apps while the salah is going on .?