I KNOW THE PAIN... the pain of having to make decisions like this. FIrst of all this is the time when extra attention needs to be given to the older child. All the gifts and parties focus on the coming baby so it is very important for the older child who is aware of EVERYTHING to feel special. This worked for me: Instead of saying "don't you think the baby is cute" or "don't you love the baby" try saying to your older child "When the baby looks at you she loves you so much" "she/he thinks you are so smart" "she/he loves it when you bring her toys and touch her softly, I can see it in her eyes".
I suggest asking the parents-in-law to come for the 3rd birthday. When a second baby comes life gets challenging again. I was not one of those mothers that handled the transition well and definitely needed space. I was figuring out how to manage life with another baby and really needed support without questioning or silent critism. If you have a history of not getting along with your husband's parents this may not be the time to invite them over. You still need support with playdates and meals and such so you may try having a friend coordinate that sort of care for you. here is a website for that: www.carecalendar.org When someone offers to help with something, don't be polite and say, "thank you but i'll be ok" write their name down before you forget who offered help and arrange for a friend to call them and let people know your needs, people don't offer a pregnant mother help to be polite!! The last thing you want is to manage other people (your parents in law) while you are trying to figure life out.
I hope the best for you. THIS is the time to take care of yourself, phisically, spiritually and emotionally... if the people around you aren't contributing to YOU then "right now" is not the moment for you to be inviting them over, cuz you might end up catering to them just to keep the peace instead of having them cater to your needs. :) ---Much love.