Scholars of Ahlus Sunnah say that only Shirk is the unforgivable sin and those who do shirk are the only people who will abide in Hell forever. But Allah says in the Quran that there are other sins which may doom a person in Hell Forever. The following are the verses in support of this.
1)"Nay, but whosoever hath done evil and his sin surrounded him; such are rightful owners of the Fire; they will abide therein."[Quran 2:81]
2)" Whoso slayeth a believer of set purpose, his reward is hell forever. Allah is wroth against him and He hath cursed him and prepared for him an awful doom"[4:93]
3) And those who cry not unto any other god along with Allah, nor take the life which Allah hath forbidden save in (course of) justice, nor commit adultery - and whoso doeth this shall pay the penalty;
The doom will be doubled for him on the Day of Resurrection, and he will abide therein disdained forever"[Quran 25:68]
How do the scholars interpret these verses which inform us that persons committing sins other than Shirk may also be doomed in Hell forever? Please explain.

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 is His slave and Messenger.

Among the established principles of Ahlus-Sunnah is that the people who had committed major sins will not abide in Hellfire forever. There are numerous proofs from the Quran and the Sunnah and the consensus of the scholars of Islam about this.

The evidence from the Quran:

Allah says (what means): {Verily, Allaah forgives not that partners should be set up with Him in worship, but He forgives except that (anything else) to whom He pleases.} [Quran 4:48) "Except that" means major and minor sins.

Allah also says (what means): {And if two parties or groups among the believers fall to fighting, then make peace between them both.} [Quran 49:9] Allaah called these groups "believers" although they were fighting each other.

Evidence from the Hadeeth:

Al-Bukhari and Muslim reported that the Prophet   said: "My son (he pointed to Hussein) is a leader and Allaah will make him settle a conflict between two great groups of believers." These groups were the people of Syria and those of Iraq. The Prophet called them believers' although they were fighting each other.

In addition to this, we have the Hadeeth of the Great Intercession (Shafaa'ah) where it is mentioned that the Prophet will interceed for those of his Ummah who committed major sins. We only cited these proofs; there are many more.

As for the verses the brother mentioned in his question, then they do not conflict with what we stated above.

The first verse you mentioned was revealed about the polytheists from the people of the Book. Allaah says (what means): {And they say, “Never will the Fire touch us, except for [a few] numbered days.” Say, “Have you taken a covenant with Allaah? For Allaah will never break His covenant. Or do you say about Allaah that which you do not know?” Yes, [on the contrary], whoever earns evil and his sin has encompassed him-those are the companions of the Fire; they will abide therein eternally.}[Quran 2: 80-81]

Al-Qurtubi (The great interpreter) says while explaining this verse: "Allaah made it clear that eternal dwelling in Paradise or Hell depends on the degree of Iman(faith) or Kufr (disbelief), not on what they ( the polytheist) said. And he said that "evil" in the verse here means: polytheism (shirk). His evidence is the following verse. {And whoever comes with an evil deed - their faces will be overturned into the Fire, [and it will be said], ‘Are you recompensed except for what you used to do?} [Quran 27:90]

The following verse was also revealed about polytheists.

Allaah says (what means): {And those who do not invoke with Allaah another deity or kill the soul which Allaah has forbidden [to be killed], except by right, and do not commit unlawful sexual intercourse. And whoever should do that will meet a penalty. Multiplied for him is the punishment on the Day of Resurrection, and he will abide therein humiliated.} [Quran 25:68-69]

"That" here refers to all the evil that was mentioned before including polytheism. This opinion is supported by the circumstances in which this verse was revealed. Some polytheists killed and went beyond all boundaries and committed fornication and adultery. Then they came to the Prophet and said: "O! Muhammad what you are calling to is beautiful above all if you inform us that there is a way for us to repent from what we committed. Then Allaah revealed the above verses and this verse: {Say,“O My servants who have transgressed against themselves [by sinning] do not despair of the mercy of Allaah. Indeed, Allaah forgives all sins. Indeed, it is He who is the Forgiving, the Merciful.} [Quran 39:53]

As for the verse Quran 2:81 Allaah says (what means): {And whoever kills a believer intentionally, his recompense is Hell to abide therein.} [Quran 4:93]

Its explanation is as follows. Abu Al-Mudhaffar Al-Sam'aani says in his interpretation: "Know that this verse is not evidence that whoever commits a major sin among the Muslims will be eternally in Hell, if we look at the circumstances in which it was revealed. The verse was revealed about a person who had killed a non Muslim. It is also said that the verse refers to the killer who considers killing lawful."

Al-Qurtubi says: "Eternally" does not necessarily mean staying permanently in Hell."

Ibn Katheer said: "Eternally means staying for a long time. There are many sound Ahadeeth that prove that anyone who has a part of an atom of belief in Allaah, he will not stay eternally in Hell, as Allaah will bless anyone who has the smallest portion of an atom of Iman by taking him/her out of Hell."

The Arabs say: "I will keep him in prison forever.", and they also say: "May Allaah keep your kingdom forever." All this means that forever does not mean eternally.

Allaah Knows best.