The point the sisters were making is that you should look at the verses that come before and after the Quranic quotes you mentioned. Let me show you what they mean
This is what you quoted from chapter 8 Verse 12:
I will cast terror into the hearts of those who disbelieve. Therefore strike off their heads and strike off every fingertip of them
And this is 8:12 and also the verse that come before it (8:11) and after it (8:13):
(Remember) when He covered you with a slumber as a security from Him, and He caused water (rain) to descend on you from the sky, to clean you thereby and to remove from you the Rijz (whispering, evil-suggestions) of Shaitân (Satan), and to strengthen your hearts, and make your feet firm thereby (11) (Remember) when your Lord revealed to the angels, "Verily, I am with you, so keep firm those who have believed. I will cast terror into the hearts of those who have disbelieved, so strike them over the necks, and smite over all their fingers and toes." (12) This is because they defied and disobeyed Allâh and His Messenger. And whoever defies and disobeys Allâh and His Messenger, then verily, Allâh is Severe in punishment (13)
This verses are talking about fighting in the battle and it is not a command to go out and slaughter any non muslim, if you want to understand more read the the rest of the chapter and i would also suggest that you also learn more about what the battle was about and etc.
And this is what you quoted from Chapter 5 verse 33:
The punishment of those who wage war against Allah and His messenger and strive to make mischief in the land is only this, that they should be murdered or crucified or their hands and their feet should be cut off on opposite sides or they should be imprisoned; this shall be as a disgrace for them in this world, and in the hereafter they shall have a grievous chastisement.
And this is 5:33 and also the verse that come before it (5:32) and after it (5:34):
Because of that We ordained for the Children of Israel that if anyone killed a person not in retaliation of murder, or (and) to spread mischief in the land - it would be as if he killed all mankind, and if anyone saved a life, it would be as if he saved the life of all mankind. And indeed, there came to them Our Messengers with clear proofs, evidences, and signs, even then after that many of them continued to exceed the limits (e.g. by doing oppression unjustly and exceeding beyond the limits set by Allâh by committing the major sins) in the land!.[] (32) The recompense of those who wage war against Allâh and His Messenger and do mischief in the land is only that they shall be killed or crucified or their hands and their feet be cut off from the opposite sides, or be exiled from the land. That is their disgrace in this world, and a great torment is theirs in the Hereafter. (33) Except for those who (having fled away and then) came back (as Muslims) with repentance before they fall into your power; in that case, know that Allâh is Oft-Forgiving, Most Merciful. (34)
I hope you understand what the sisters are talking about, we cant just quote just one verse of the Quran and try to understand what it is saying. It is very important to read what comes before it or after or even the whole chapter to understand a certain ayat(verse) of the Quran. I hope this answers your question. If our answers are not enough for you, i suggest that you do your own research and if possible ask someone who is well versed in the Quran.
