If my parents do not pray, or do not pray much, and I pray for Allah to forgive them and reward them and to ensure they never suffer or face pain after dying, will this be accepted inshaAllah?
Your praying and wishing goodness for your parents is a good deed. However, Allah the Almighty takes everyone to account for his/her own self. Your parents must fulfill their duties towards Allah; and you can warn and advice them but your prayers will not substitute for theirs.
“Oh people! Be conscious of your Lord, and fear a Day when no parent can avail his child, nor can a child avail his parent, in anything. The promise of God is true. Therefore, neither let the worldly life deceive you, nor let the Deluder delude you concerning God.” (31:33)
“Prepare yourselves for a day where no one shall avail anyone in any way, nor shall an intercession be accepted from anyone, nor shall anyone be acquitted for any ransom, nor shall the guilty ones be helped.” (2:48)
We wish that your parents take to the right path. Keep reminding the verses of Qur’an to your parents, and keep warning and also praying for them. However, you cannot enforce them to perform their worships. Do not feel yourself responsible for their wrong choice. Even Prophet Muhammad (p.b.u.h.) was not able to direct some of his closest relatives to the right path. He kept trying, though.
“We are fully aware of what they say; and you are not a dictator over them. So, inform with Qur’an whoever fears my promise.” (50:45)