Wa alaykum salam,
Note that, in the Sunni traditions, though the practice of taraweeh is greatly upheld by the Sunni brethren, it is not fard /wajib. Rather it is considered as a deed of sunna muakkida; a highly stressed tradition.
As for the Shia Tradition there is no practice from the Imams of Ahlu Bayt a.s. on the performance of tarawih as is being done by the Sunni brethren.
For us the traditions have mentioned specific numbers of units of prayers to be done on each night of Shahru Ramadhan. For details refer to the books of recommended prayers. Note that as these prayers are mustahab /recommended they cannot be performed in Jamaah / congregation as is being done for taraweeh.
From the foregoing you need to consider the following:
Do all the Sunnis perform the taraweeh?
As for the Sunnis who do not perform taraweeh are they considered to have committed a sin and a cause of disunity?
Likewise as a Shia, do you think that the unity is truly maintained by only praying the tarweeh with the Sunni brethren?
Are you gaining reward to perform the taraweeh and ignoring the guidance from the Ahlul Bayt a.s.?
Is this not an opportunity for you to strengthen the relations through being honest and explaining your position as a Shia with regards to Taraweeh prayer?
Our respected maraji, including Ayatullah Al Udhama Seyyid Ali Seestani, have always advised us about interacting with sunni brethren on basis of love and respect. An expected outcome of these interactions is the exchange of knowledge especially with regards to the variations in the beliefs and practices between each other. This will overcome the ignorance and prejudice amongst each other. It is through strengthening this relationship that the rationale for the various differences in fiqh can be discussed and mutually appreciated without offending each other. This scenario where you are a minority amongst the Sunni majority is common throughout the world. This provides an opportunity to enlighten the Sunni group on the shia fiqh with regards to the Taraweeh.
Consequently rather than compromising on our faith and practices so as to 'show solidarity' one needs to confidently practice our faith especially where there is no justification to abandoning it or modifying them. Solidarity is not about unification, abandoning and compromising. Rather it is about accepting differences, respecting each other and appreciating diversity.
Fazle Abbas Datoo