All perfect praise be to Allaah, The Lord of the worlds. I testify that there is none worthy of worship except Allaah, and that Muhammad, sallallaahu ‘alayhi wa sallam, is His slave and messenger.
Undoubtedly, not observing the prayers is one of the grave major sins, and some scholars even considered those who do not pray as disbelievers. Also, not adhering to Hijab is also considered a grave major sin, as Allaah Says (what means):
* {and do not display yourselves as [was] the display of the former times of ignorance}[Quran 33:33]
* {O Prophet, tell your wives and your daughters and the women of the believers to bring down over themselves [part] of their outer garments.}[Quran 33:59]
Thus, you have to advise them and tell them how dangerous these sins are. You can also give them charity if they were in need, provided that they would not spend that money on prohibited things.
On the other hand, we do not advise you to bargain with them as this may lead to aversion and stubbornness. You should advise them gently and offer them presents, such as useful tapes or booklets, which may reconcile their hearts.
You should know that if you do all this for the sake of Allaah, it would be added to your record of good deeds. The Prophet, sallallaahu ‘alayhi wa sallam, told us that guiding one person to the right path is better than the most precious treasures. [Al-Bukhari and Muslim]
Allaah Knows best.