The question of whether it’s morally blameworthy not to devote your whole life to reducing suffering conjures the wrong idea. Utilitarianism is not a binary morality in which you’re right if you do the best possible thing and wrong otherwise. Rather, utilitarianism is more like a point counter in a video game, where you aim to accumulate as many points as you can within the bounds of reason. There’s no binary “right” and “wrong”. You just do the best you can.
Relatedly, the idea of a “moral obligation” is not intrinsic to utilitarianism. Talk about “duties” and “requirements” is a way humans communicate when they want to motivate others strongly to perform some action. “Rightness” and “wrongness” judgments are useful instrumentally as a way to motivate good behavior.
Thus, to call someone “morally blameworthy” unless she gives up her family and friends to devote her life to reducing suffering is a self-defeating strategy. It would be like creating a club with a $10 million membership fee. Sure, you might get a few members, but in order to appeal to a broad audience of people who can be helping with the cause, the bar has to be much lower.
In addition, it’s a mistake to think like this: “Setting a low bar is just a way to make sure more people help, but once I joined the cause, I’d see that demanding vastly more of myself would be much better than just doing a little bit. Therefore, this cause is too demanding, and I won’t join.” This is precisely Edmund Burke’s fallacy. If imagined excessive duties prevent you from accepting utilitarianism, those excessive duties were not a utilitarian recommendation to begin with. Rather, you’re making an error.