The following is the traditional Jewish understanding of Amos 9:1-2 as per the Da'at Mikra of Yehuda Keil et al.
1.p1 "I saw the Lord present at the altar" - Amos says, in a prophetic vision I saw the Lord's presence besides the altar... of the temple at Bet El, whose adherents mistakenly believed in a doctrine that the Lord was in some way physically present to accept their sacrifices. The language is ironic.
1.p2 "And he [the Lord] said to me strike the lintel such that the door posts will quake [same word as used for earthquake]" - A possible allusion to the story of Samson. This is apparently a prophecy of an earthquake.
1.p3 "And [you, Amos] break them [the door posts] on the heads of all [those assembled], and anyone [of the assembled] who survives, I [the Lord] will kill by the sword." - This is apparently a prophecy of war following the earthquake.
1.p4 "Not a single [would-be] escapee [of those assembled at the temple] will [in the end] escape, not a single [would-be] refugee [from those assembled at the Bet El temple] will in the end get out" - The verse is alliterate by using the same root for noun and verb forms of escapee/escape and refugee/to seek refuge.
2.p1 "If they [those who were assembled at the temple and now seek to escape from the earthquake and war] dig deep [seek refuge in caves, as was commonly done during wars], from there [the caves] my hand [the Lord's hand] will take them."
2.p2 "If they will try to climb up to the sky [apparently a general reference to high places such as Mt Carmel mentioned in the next verse that were high, heavily forested and had deep caves], from there I will bring them down." See similar language in Obadiah 1:3-4.
The temple mentioned in verse 1 is the Bet El temple, as this is a prophecy of doom specifically on the northern kingdom of Israel and the house of Yeravam (e.g. Amos 7:9,13). The verse hints that the main force of the destruction is directed specifically at the adherents to the Bet El sanctuary and its doctrines.
The Hebrew of these verses in the masoretic text is poetic and telegraphic, but not particularly difficult to understand. There is only one word, the word used for "break" in verse 1.p3 that is unique and unusual.