For three or four endpoints all within the home, you could do this with just ATAs and not even need a SIP server. Many ATAs have a configurable "dial plan" that will let you map a number to an IP address, thus giving you the ability to call the other terminals directly within the LAN.
Janky is directly proportional to cost. Grandstream are the jankiest and least expensive. I like the Cisco 191; it is a fine unit but costs about $100-120.
