We're doing diapers only since it's SIL's 3rd baby so that's why they didn't want to just watch her open presents.
You are asking how many and/or what type of games are appropriate for a diaper shower for a third baby? This should go over well.
Since it's too late for you to say "no games - and no diaper showers, and no third baby showers", just nix as many games as the family will allow. Four is way too many. As it stands, I would make up an excuse to leave a party like the one described - assuming we're in an alternate universe where I attend a diaper shower for a third baby.
Last but not least, although you didn't ask, a simple way to avoid this issue in the future is to not host any more diaper showers for third babies...