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.
You must thank Allaah The Almighty for enabling you to comply with His Obligations and adhere to the straight path, because one of the greatest favors of Allaah is enabling His Slave to obey Him.
Also, you must explain to your uncle that underestimating death and Hell is considered ridiculing the promise and punishment of Allaah, which contradicts a person's belief in them, because belief in Allaah’s Promise and Punishment means glorifying and dignifying them. His statement, "he does not fear entering Hell" certainly contradicts this glorification.
Many scholars stipulated that whoever ridicules the promise and punishment of Allaah The Almighty is an apostate and a non-Muslim, as stated by the Hanbali scholar Al-Buhooti . Thus, your uncle must repent to Allaah from this serious statement. He must also understand that the prayer is of great importance in Islam and whoever abandons it has no share in Islam.
Besides, you must do your best to advise them and seek the help of those who may have influence on them. Also, use the booklets and tapes that explain the ruling on abandoning the prayer and that this is disbelief that takes a person out of the fold of Islam, even if one abandons the prayer out of laziness, according to the scholars.
You should put all your efforts on this issue. Likewise, concentrate on the issue of the Hijab with your aunt and explain to her that a woman her age is obliged to wear the Hijab. According to the consensus of the Muslim scholars which is supported with the texts from the Quran and the Sunnah, when a Muslim woman reaches puberty she must abide by all Sharee'ah obligations, including the Hijab.
Allaah Knows best.