Sorry if this ends up being a bit long.
First I need to give a bit of background. First off FI and I are paying 100% for the wedding. None of our parents are helping in any way, which is totally fine. My mom and dad have been divorced since I was a year old, so for 30 years! My dad was pretty much out of the picture about 90% of my life until I was in high school. My freshman year of high school I went to live with him and we developed a better relationship. We have a pretty good relationship now for the most part. (It does bother me that my dad pretends to have always been this amazing and wonderful father even though years went by when we didnt see or even speak to him bc we were not a priority.)
When I was around 8 years old I found out that I have a half sister and half brother who are 10 and 12 years older than I from a previous relationship that my dad had. I spoke to them on the phone once or twice growing up at Christmas but that was it. When I was a senior in high school my dads mom passed away and I met them for the first and last time. I havent seen or spoken to either on of them in over 13 years. In January my half sister was diagnosed with cervical cancer. I guess she and my dad started talking a lot more after she was diagnosed and had to have a hysterectomy. My dad started really pressuring me to talk to her but I have no desire to. She is a stranger to me and I have no desire to have her as a part of my life. She lives a very different lifestyle than I do and I choose to have to deal with that kind of drama. I have completely cut ties with two of my older brothers for the exact same reason.
Last month my dad showed up at my daughters birthday party and had a woman with him that I didnt recognize. It was my half sister. It was extremely akward for me and I was really upset that he didnt even tell me he was bringing her. My daughters were confused about who this random person was trying to take millions of pictures of them and asking them all kinds of questions and so were my friends and my FI. I didnt say anything to my dad about it bc I didnt want to cause a big huge fight. I just planned to continue not contacting her.
Now for my dilema...Today I called my dad just to check in and see how things are going. I asked him if he had gotten his invitation in the mail and told him that if he hadn't it should be there in the next day or so. He then asked if I had any extra invitations left. I said maybe 1 or 2 and asked why (thinking maybe he wanted an extra to save or something). He said that my half sister really wants to come to the wedding. I didnt even know what to say so I just said I would have to wait and see what happens with our other guests bc we are already at capacity for our reception venue and we cant invite one more person at all unless someone else were to decline (which I would never normally do...I dont have a "B" list). I was 100% telling the truth. We really dont have room for any more people at all. I really don't want her to come.
She is a complete and utter stranger to me for the most part. I also feel like if I invite her she will show up with her 10 children and their children as well (no, I am not exaggerating at all...she has 10 children and 5 grandchildren at 43). There is absolutely no way that we can fit 1 extra person right now, let alone 16! We gave every single person a plus one to the wedding bc we thought that was the most fair way to do it. My dad originally was going to be bringing his serious girlfriend but I guess they are having some relationship problems so he asked that I not put her name on the invitation. I am almost positive that even if I dont send her an invite my dad will bring my half sister as his guest. I know its his choice who he wants to bring but I think it really unfair of him to put me in this position. I dont think he should be trying to force me to have a relationship with someone when I do not want to, especially when he knows how I feel about that kind of thing. I want to flat out tell him that she is not invited. Anyhow...if anyone has any advice about how to handle this I would really appreciate it. Thanks for letting me vent too!
ETA: I should also mention that I am not inviting my two older brothers or any family from my moms side at all. They are not a part of my life and I have zero contact with them, by choice. I know that if I invite my half sister, whom I dont even know (I dont even know her last name), it is going to upset my mom (bc if I am inviting her why would I not invite my borthers) and it will cause drama that she will have to deal with involving my 2 older brothers.