If I don't make a big difference outside of my immediate household, have I fulfilled God's plan? How would I know. And is it okay to forsake, at least temporarily, helping any others, for the sake of helping only those within my immediate household, if I think the needs are 'great enough.' How can I determine whether its truly enough, or the needs pressing enough, to limit my sphere of influence to those only within my own family (wife, son, 2 dogs).
I encourage you to read about St. Therese of Lisieux... God works through us, even in our very "little" sacrifices - when we focus on who we are truly doing them for - Jesus.
Ask God to GIVE you others to help - constantly... in the ways that only He knows best.
Don't fret about the grandeur of your works, as long as it's done with the grandest of love.
Your first responsibility is to your family, every time. We never know how much of difference we make with whatever effort we make. An off hand remark or a spontanous two dollar donation to a street bum can change a life forever and a generous charity donation can end up in the pocket of a con artist. It’s best to do what you can and leave the rest to the Holy Spirit!