Wendy - I think as long as you have already started informing the people that you are inviting, then later just follow up with the invite, think it's ok lah. Small problem, don't get too stressed up. We'll have bigger problems when it comes to seating arrangements!
Think this is a super stressful period for all of us. J Tan - I think we cannot please everyone, you have to sacrifice someone. One person unhappy better than everyone unhappy. For me, I sacrifice my MIL for my mum's happiness. They are also sitting at separate tables. MIL not happy too, actually quite mad but I really couldn't care less. Think if your father is so insistent, your in laws have to give in lor.
Jelly - Good luck to you! Hope u will solve your technical issue soon. Dun worry, still have some time left. Will sort out one. Stay cool!!