Hi,
I am assuming that your wife is happy in the truth and wants to continue as part of the congregation.
Firstly, don't get angry with them, they are used to that all the time from people in the ministry, they are trained to deal with that and it will only work against you. Smile pleasantly when you speak to them, talk slightly quiter than you would normally, speak to them as you would if you were asking someone directions or a favour, tell them you want to be there to support your wife and that you respect her beliefs and that you want do what you can to support her efforts in the truth because you know how much it means to her. This will throw them off balance a bit and they may at that point decide it would be a good thing for you to be there, especially if they think they might be encouraging you along in the process.
But you don't really need to show them anything, turn the table on the elders, all you have to do is go with her and tell them to show you where it is stated in scripture that you are not allowed to be present, but don't be agressive about it, according to their own words in the marriage vows you and your wife are one as stated in Ephesians 5:31, weather you are a believer or not does not alter the order of subjection, the wife is in subjection to the husband, the husband is in subjection to the Jesus Christ and Christ is in subjection to Jehovah God, oops, did I leave the elders out, although it states that the congregation is subject to Christ this is refering to the fact that the congregation is answerable to Christ, it does not mean the elders can jump in between the wife and husband in the order of subjection.
If it is a matter that could involve being disfellowshipped bear this in mind, they can not disfellowship anyone as a form of punnishment no matter what anyone does, if someone states that they are truly repentant the elders have to believe them, if however the person in question repeatedly commits the same sin, (for example if someone says i'm sorry I genuinly regret my actions in robbing that bank, but then they go and rob another one a week later) then it will result in being disfelloshipped. According to the organisation disfellowshiping should be the last resort that they take to keep the congregation clean if, and only if, the person is unrepentant.
One last bit of advice for both of you, elders are very good at the way they ask questions, they will try and trap your wife, stay calm and cool, keep the answers as short and to the point as possible, pause before you answer them, if they look as though they are trying to trip your wife up by asking leading questions calmly say to them, I thought that your purpose was to help my wife spiritually to gain a good standing in the congregation and with Jehovah, not to push her away. Play to there ego, they love having there ass kissed, tell them your both there because you want their help, their guidance not to fight against them.
I was in the "truth" for 50 yrs but enough is enough, personally I'd tell them to go forth and multiply, but if ther's anything I can do to help your situation I will try and give what advice I can.