Feeling bad about telling my sister she can’t bring her BF to our micro wedding

We originally wanted to elope but decided on a micro wedding so we could share the time with our closest friends and family. We are doing a wedding on a private property renal and a restaurant reception in another town after. Our “venue” capacity is 8 but we got permission from the hosts to have 10-12 for just the ceremony. We are inviting our parents (4), MOH and her BF (2), Grandparents (2), officiant, photographer, and Siblings + SIL (3) which brings us to 15 people including us if everyone comes. We know 1 grandparent won’t come and 1 might but we are unsure. Fiancés sibling and wife also said they are not interested but we are inviting them anyways.

We initially told my sister she couldn’t bring her bf to the ceremony due to being over capacity but we would be happy to have him at the reception. We would never say this to her face but she also has a bad track record with relationships and we didn’t want a stranger in all our family photos. I am starting to feel really bad about this tho because it is asking her to celebrate our relationship while snubbing hers. I don’t know if this is relevant but her relationship is new and we haven’t met him while everyone else we are inviting we have known for years and are extremely close with. It was really hard to pick who got invited and we already have many friends and family mad they are not invited.

Should I invite her BF and just hope we get enough RSVP declines to make it work or am I overthinking this?