First up, this:
On point (a), I will note that 'those who pierced him' includes Gentiles:Revelation 1: 7 Behold, He is coming with clouds, and every eye will see Him, even they who pierced Him. And all the tribes of the earth will mourn because of Him. Even so, Amen.
Matthew 24: 30 Then the sign of the Son of Man will appear in heaven, and then all the tribes of the earth will mourn, and they will see the Son of Man coming on the clouds of heaven with power and great glory.
Notes:
a. “those who pierced him” = Romans (John 19:34-37).
b. “all the tribes of the Land will mourn” = Israel (Matt. 24:30,34) (Zechariah 12:10-14).
The 'they' in this context is clearly the Roman soldiers who were looking at Christ to see if he was dead. They were the ones who pierced him, and it is their inspection of Christ to which these two Old Testament passages are applied.Johnn 19:
32 So the soldiers came and broke the legs of the two men who had been crucified with Jesus, first the one and then the other.
33 But when they came to Jesus and saw that he was already dead, they did not break his legs.
34 But one of the soldiers pierced his side with a spear, and blood and water flowed out immediately.
35 And the person who saw it has testified (and his testimony is true, and he knows that he is telling the truth), so that you also may believe.
36 For these things happened so that the scripture would be fulfilled, “Not a bone of his will be broken.”
37 And again another scripture says, “They will look on the one whom they have pierced.”
Now to point (b). The phrase translated 'tribes of the earth' is the Greek phrase PHULAI THS GHS. This means 'families of the earth'. It does not mean (as is claimed here), 'tribes of the land [of Israel]'.
It should be noted that this Greek phrase does not occur in Zechariah 12:10-14 (which you quoted).
In the LXX (the Septuagint, the Greek translation of the Hebrew Scriptures), the phrase PHULAI THS GHS is used consistently of the Gentile nations outside Israel - it is not used of 'the tribes of Israel':
This establishes the meaning of the phrase PHULAI THS GHS. It does not refer to the 'tribes of Israel', it refers to the Gentile families of the earth.Genesis 12:
3 kai euloghsw touv eulogountav se kai touv katarwmenouv se katarasomai kai eneuloghyhsontai en soi pasai ai fulai thv ghv
Genesis 12:
3 And I will bless those that bless thee, and curse those that curse thee, and in thee shall all the tribes of the earth be blessed.
Genesis 28:
14 kai estai to sperma sou wv h ammov thv ghv kai platunyhsetai epi yalassan kai epi liba kai epi borran kai ep anatolav kai eneuloghyhsontai en soi pasai ai fulai thv ghv kai en tw spermati sou
Genesis 28:
14 And thy seed shall be as the sand of the earth; and it shall spread abroad to the sea, and the south, and the north, and to the east; and in thee and in thy seed shall all the tribes of the earth be blessed.
Psalm 72:17 (71:17) estw to onoma autou euloghmenon eiv touv aiwnav pro tou hliou diamenei to onoma autou kai euloghyhsontai en autw pasai ai fulai thv ghv panta ta eynh makariousin auton
Psalm 72:17 (71:17) Let his name be blessed for ever: his name shall endure longer than the sun: and all the tribes of the earth shall be blessed in him: all nations shall call him blessed.
Ezekiel 20:
32 kai ouk estai on tropon umeiv legete esomeya wv ta eynh kai wv ai fulai thv ghv tou latreuein xuloiv kai liyoiv
Ezekiel 20:
32 And it shall not be as ye say, We will be as the nations, and as the tribes of the earth, to worship stocks and stones.
The Revelation does not therefore use the phrase PHULAI THS GHS to refer to the tribes of Israel.
When it does refers to the tribes of Israel, it uses the Greek phrase PHULWN UIOS ISRAEL - which means, wait for it, 'families/tribes of Israel'.
Let me know if the Greek isn't displayed in the correct font (it's OLBGRK).