Welcome! First let me say, I agree w/ everything everyone else has previously said.
But I get the impression you want to know how this will be handled w/i the KH. My impression is that you do not wish to make it your day, but would rather allow your family member to proceed with their wedding without the JW drama. If that is the case, that is very loving on your part, because JWs will not be so loving towards you and you should be prepared for the cold shoulder and shunning process that will take place.
In some cases, family members who are JWs who have DF'd/DA'd family members have excluded them from the wedding/reception. Be prepared. Should the elders not give your father grief over his inviting you, and you went to the KH for the wedding, then I believe most JWs would see it as disrespectful for you to sit up front. Keep in mind the keeping to the back of the hall thing is a show of respect and humility (of course BS, but whatever) and that is why the procedure is followed by many.
Again, I agree with what was said previously, you can sit where ever you want. But again, if you are trying to be respectful of your father, you may want to ask your father what he would feel comfortable with what you do.
Either way, good luck to you and whatever you decide to do.