Ahsanallahu ilaykum , May Allah reward you and your family abundantly Is it permissible for one to pray with singlet ? Is it obliged to marry a woman/man his/her parents are forcing one to marry ?

Singlets refer to different things sometimes. Do not pray in something that does not cover the awrah and shows its shape. Also cover your shoulders. As for marriage, if you do not want that person, obeying your parents in it is not obligatory, so you do not have to marry that person. Marry the one you choose, but speak to them kindly until they accept.