I would offer the meal, and of course, if they are truly not in need of a meal, they will be polite and say, "Oh, dear we interrupted your meal! We can come back another time!" However, not everyone is willing to share their circumstances, even with good friends. Perhaps they are truly in need? Perhaps they dropped by for expressly this reason, their children are hungry and they don't have the funds to feed them properly, and they know you feed your family at this time. People don't always tell us face to face they are hurting and need help. My suggestion is to help them no matter what. Offer the meal, and open some cans of vegetables or heat some frozen veggies to stretch the meal. Toast some bread or warm some rolls in the microwave, anything to stretch it. Sometimes, it's just a test from God to see if you will do. Of course, that is just my personal opinion.

Revelations 3:20 Behold, I stand at the door, and knock: if any man hear my voice, and open the door, I will come in to him, and will sup with him, and he with me.