MB4 263b: You and Your Items in Different Cities and Hilchos Techumim (397:17-18); City Borders and Techum (398:1)

If someone has his items in another city outside his techum but he and the items are within someone else's techum, can they bring him the items?

If one invites guests on Yom Tov and they have a different techum, can they bring food back to their house?

One's "four amot" include his city of residence for Shabbos. The techum only begins at the edge of the city in all directions. How are the 2000 amot calculated?