How do i communicate to my family that their expectations are too high?

I don't really think you can. If they won't truly listen to what you are telling them and can't accept that their way is not the only way to family, then there's not really anything you can do to change their minds. Hopefully they will gradually accept that there are different ways of being in this world.

Just keep your messaging consistent, being careful never to express to your family that you also wish your FS would join in more (it's fine that YOU feel this way, but if you share your feelings with them, they will never let up). Be positive and brief, and then change the subject whenever they bring it up.

Step up and put your foot down. They're trying to make him act like someone he isn't and these guilt trips they're pulling on you are uncalled for. Make it clear that things are the way they are and they'll either have to accept it or see less of you. You're marrying into his family also and I'm sure they aren't pulling the stuff your family is to make you into someone you're not.

Be firm and set and maintain boundaries with consequences. Get used to saying no now before the marriage starts so that you have practice in down the road when other life decisions pop up. While your fiancé is marrying into your lively social family, there needs to be a balance. If they are not willing to listen now and are pressuring you out of your comfort zones, then unfortunately there is nothing you can say or do to sway them outside of going no contact which is not an option in your case.

Would you be comfortable with telling them if they don't knock it off you won't be coming around as much because you don't like the way they are guilt tripping you and trying to make him do something he's not comfortable doing? Sometimes that is what it takes.

If a woman was on here saying the same thing about her fiancé's family, a lot of people would say he is too enmeshed with his family of origin. This causes healthy boundaries not to form. You have already expressed one. They keep complaining about his perfectly normal behavior even though you have repeatedly asked them not to. This is likely to be a problem in your marriage. What if he doesn't agree with your family seeing a newborn at the hospital. What if he doesn't want to spend every holiday with them? You really need to set some healthy boundaries with your family asap.

You have a few options. One poster already mentioned one - tell them if they don't knock it off, they'll be seeing less of you, and mean it.

My other suggestion:

Stop responding to the behavior altogether. Literally stop. Don't explain. Don't even answer. Remember how people used to say, a good way to deal with bullies is to ignore them? Don't give them the satisfaction that their guilt-trips are working on you (because they are - that's why you keep answering to them, and why they think they're effective.)

Try something like this:

Family: Where is FH?
You: He didn't come with me today.
Family: He needs to step up and be a part of the family!
You: The most hilarious thing happened to me at the office yesterday.....

If they continue to push after the first redirect, just keep at it. Think before you go about a story you can tell, or something you can derail them with ("mom, what was that thing you were telling me about on the phone the other day?") This is effective for multiple reasons - it isn't giving their behavior the reinforcement they're looking for, and it puts them in the uncomfortable position of recognizing that you aren't putting up with it.