Your question somewhat amounts to two separate questions. Though, perhaps there is some reason you asked them together (besides their proximity) that I am not grasping. In any event, I chose to treat each question separately.
Spiritually or Symbolically
The word translated variously as "spiritually" or "symbolically" or "metaphorically" is πνευματικῶς. The only other exact instance in the New Testament is found in 1 Cor. 2:14. The ESV reads (emphasis mine throughout), "The natural person does not accept the things of the Spirit of God, for they are folly to him, and he is not able to understand them because they are spiritually discerned." It seems translations that use "symbolically" are treating it as a gloss. Both the ESV and the NET footnote that the Greek is "spritually", which is readily understood from the prefix, "πνευμα".
Commenting on the Greek text, Beale states:
πνευματικῶς (“spiritually”) shows that the city is not to be understood in a literal, earthly manner, but figuratively through spiritual eyes (so likewise πνευματικῶς in 1 Cor. 2:14). The city is ungodly and is not to be located in any one geographical area but is any ungodly spiritual realm on earth. Of course, if the city is assumed to be a literal Jerusalem, then πνευματικῶς must refer only to the spiritual character of that city.
Beale, G. K. (1999). The book of Revelation: a commentary on the Greek text (p. 592). Grand Rapids, MI; Carlisle, Cumbria: W.B. Eerdmans; Paternoster Press.
I would tend to favor the reading of "spiritually" since the referent of "sybmolically" is not clear. The great city is not a symbol of a literal Sodom and Egypt. The great city has the character of Sodom and Egypt. That is, spiritually speaking, it is comparable to the two of them. For this reason, I would think it is better to omit the gloss and simply render this as "spiritually" rather than the alternatives.
In the end, this comes down to translation philosophy more than anything.
Our Lord or Their Lord
The King James is based on the Byzantine text type, which indeed supports its reading of "our Lord":
και ο κυριος ημων εσταυρωθη
However, the older manuscripts support the reading "their Lord" found in modern English bibles. For instance, P115 reads like so:
και ο κ̅υ̅ αυτων εσταυρωθη
Vaticanus likewise supports this reading. Sinaiticus omits either word, but has αυτων as a correction.
None of the more relatively recent commentaries that I checked (NIGTC, BECNT, HK) even mention "our Lord" as an alternative reading (not even Metzger's). Barnes does note, however:
The common reading of the text here is “our Lord” - ἡμῶν hēmōn. The text now regarded as correct, however (Griesbach, Tittmann, Hahn), is “their Lord” - αὐτῶν autōn. This makes no essential difference in the sense, except that it directs the attention more particularly to the fact that they were treated like their own Master.
The textual evidence seems to favor the reading "their Lord" rather strongly.
The internal evidence, in my estimation, likewise points to "their Lord" as the better reading. A search for references to "our _" reveals the use of the first person plural genitive in only two scenarios. The first is in the introduction to the letter, where John writes in 1:5 (AV), "Unto him that loved us, and washed us from our sins..." Once John begins to describe his visions, however, we do not see the use of this again (bracketing 11:8 for the moment) except on the lips of the characters in his vision." The third person genitive, however, appears throughout the text in John's narration. For example, 6:11 (AV) says, "And white robes were given unto every one of them; and it was said unto them, that they should rest yet for a little season, until their fellowservants also and their brethren, that should be killed as they were, should be fulfilled." The Authorized Version does also render the final verse, "The grace of our Lord Jesus Christ be with you all. Amen."
In other words, when John is writing directly to the seven churches using the second person plural, he will then use the first person plural genitive. But when he is describing the visions within the bulk of the letter, he uses the third person plural genitive. While it's possible the author makes an exception here in 11:8, stylistically it would seem to break the flow of the visions to interject a statement about "our Lord" into the text.
The evidence both external and internal favors "their Lord" as the original reading of 11:8. Interestingly while many commentators assume that "their Lord" is parallel to "their bodies" in referring to the two witnesses (with which I agree), G.K. Beale (NIGTC) takes "their Lord" as referring to Sodom and Egypt. As Barnes notes above - in the case where "their Lord" refers to the Lord of the two witnesses, it makes little difference how this is translated. But if Beale is correct, it could have some interesting implications.