In this work, the fluid limit approach is applied to find stability conditions of two models of queueing networks with interacting servers. We first consider a two-station queueing model with two customer classes in which customers that are awaiting service at any queue can move to the other station, whenever it is free, to be served there immediately. Then we consider a cascade-type three-station system in which the third station, whenever it is free, can assist the other two stations. In both models, each station is fed by a renewal input with general i.i.d. inter-arrival times and general i.i.d. service times. keywords: cascade networks, fluid limit approach, interacting servers, stability, X-model.