Depends on what you mean by historically. For a long time Belarus and much of Ukraine was Lithuanian.
Should they be reunited with Lithuania?
No. But Belarus and Ukraine were and are East Slavic, not Baltic like Lithuania. Ethnically, Moldova is Romanian. It was originally part of the Romanian pricipality of Moldavia, same as Wallachia, and Transylvania. Modern Moldova, then known as Bessarabia, was taken by Russia from Moldavia in 1812 following a war between Russia and the Ottoman Empire.