Can I pray behind ithna ashara?

Thank you for your question! Although I am not authorised to issue fatawa, there are a number of considerations:

First, we have addressed the issue of praying behind a Twelver here . 

Second, the issue of taqiyya is one that has often been misused, in my opinion. It definitely has a basis in Islamic Law; however, its conditions and that which necessitates its use have a basis as well. I would like for you to think about something: Compare the situation of those Muslims of the past who were forced to use taqiyya to avoid death, loss and torture with those Muslims of today who flippantly invoke taqiyya to avoid questionable looks. My heart goes out to those who belong to the first group! With all due respect, one cannot be compared to the other. Even to this day, converts to Islam or to a particular school within Islam have to conceal their faith to avoid very real threats to their lives, bodies and property. May Allah alleviate their situations! Think about this and consider it well when invoking the use of taqiyya.

Third, I know that everyone's situation is different. As you said, you may experience emotional difficulty or ruin the reputation of your father. I don't want to belittle your situation. For that reason, I would advise (This is not a fatwa, mind you!) you to perform the actual prayer by yourself, following the fiqh of Ahl al-Bayt, and when you stand behind a Sunni/Shia, you follow them in their prayer actions, without intending the prayer. 

I say this because some actions that others perform in the prayer actually invalidate the prayer according to us based upon explicit statements of the Prophet and imams, upon them be peace. Some examples are the recitation of Ameen and the omission of the Basmala. If you feel compelled to perform such actions in order to fit in, I would advise you to perform your actual prayer alone or at home and then mimic the prayers of those you pray with in congregation without intending the prayer.

Hopefully this helps! And Allah knows best!

IRS