I also got that impression. After the attempt on Michael's life, we see Deanna outside in her nightgown running around, shouting hysterically about dead gunmen outside her window; and there is what looks to be Fredo, in his bathrobe and slippers, trying to rein her in. I assumed from this that their house must be on the grounds; but then again they could have been staying in a guest house at Michael's invitation if they had driven all the way from Vegas (or wherever they were).

Also, in the GF2 draft script at www.imdb.com , when Michael goes to ask his mother about what Vito thought deep in his heart, it describes Michael as walking through the snow to "... the house next to his own. Int. Connie's house - day. This is the house where Mama lives with Connie's children, Connie so rarely is there." (In the final script, it's just called "Mama's house on the compound.") I gather that because Michael didn't approve of her marriage to Merle, Connie and Merle lived elsewhere. They obviously are no longer together at the end of the film, which allows Connie to now move back to the estate.
Yes, wasn't that generous of him? I wonder what Mama was told every Christmas, Thanksgiving, and Easter when Fredo never showed up for dinner. (I guess if he were in New York or someplace he could always say he couldn't get a flight .)