I expect a lukewarm reaction from my in-laws and mom. My in-laws just can't fathom having so many kids. DH is an only and his SD has no bio-kids at all. I think my mil worries about how she will be able to put money in a college acct for another grand kid, she said as much when we had dd3 (it's really nice that she does that, but it's certainly not a requirement, and not a reason for us to seriously consider not having more, I think!) and I think she worries about being overextended as a Gma. Which I can appreciate, but that's really not our problem! She's a pretty great Gma and MIL, besides her tendancy to think the world revolves around her just a tad I don't think she has much to worry about.
My mom is catholic, so it's not as if she's against big families. She just kind of plays her cards close to the vest. I'm like that too. I'm just empathetic about this type of thing, so when people tell me "I'm having a baby"- I always say congrats and awesome first, and then I may say something like, "is your family excited?" or "how do you feel about having another little one?" because I KNOW how others can make you make you feel, and that when people are like that it's hard to have a safe non-judgemental space to talk about your feelings- whether it's absolute unmitigated joy, or if they come with apprehensions. You get to have that. You get to want a ton of kids, or not AND be unapologetically happy, or ambivalent about it. And you should still get support from the people you are close to. *steps off soap box*
My sister will be happy for me