If a Muslim does not pray Taraaweeh, there is no sin on him for that, whether he has an excuse or not, because it is not obligatory. Rather it is a confirmed Sunnah which the Prophet (peace and blessings of Allaah be upon him) did regularly and encouraged the Muslims to do as he said: “Whoever prays qiyaam in Ramadaan out of faith and in the hope of reward, his previous sins will be forgiven.” Narrated by al-Bukhaari, 37; Muslim, 760. 

But the Muslim should not neglect Taraaweeh prayer. If he cannot pray it with the imam in the mosque, then he should pray it at home. If he cannot pray eleven rak’ahs then he should pray as much as he can, even if it is only two rak’ahs, then he should pray Witr. 

And Allaah knows best. 

With regard to breaking your fast with the Shi’ah and Isma’ilis, if you think that breaking your fast with them will serve the purpose of softening their hearts and calling them to follow the Sunnah and give up the innovations that they are following, then this is something that is prescribed in Islam.  

But if you think that your breaking your fast with them will not serve any purpose, then it is better not to break your fast with them, and to avoid them, so as to denounce the innovations that they are following and lest they confuse you with their specious arguments when you do not have enough knowledge to realize that what they are saying is false, thus exposing yourself to fitnah (temptation, tribulation). 

And Allaah knows best.