As I understand it, the prior owners can't claim these after moving out. However, they _can_ legitimately take with them anything that isn't affixed to the house with them when they move out. Dishwasher is attached to the plumbing, which makes it officially part of the house. A ceiling light fixture is wired in, so it's part of the house. Fridge and stove are generally just plugged in so they aren't. (I have no idea whether a fridge with an ice maker/cold-water connection is or isn't.) 

If they don't take it when they move out, then after you purchase the house it will *probably* be considered abandoned, become your property, and you can do whatever you want with it. But this is one that I would ask the seller to guarantee... or ask a local real estate lawyer or real estate agent... and try to get them to put in writing.

Note that I said "legitimately". There have been instances where evicted tenants took things they weren't supposed to, or have damaged the building as a protest against the eviction. You could sue them for this, but if they're being foreclosed on that may be a waste of money. I'd instead ask my lawyer (you _are_ using a lawyer's assistance in this purchase, right?) to make sure the terms of sale say that if this happens it's the seller's responsibility to restore the house to the expected condition, rather than making the sale an unqualified "as is at time of signing" or other not-our-problem phrasing.

A foreclosure purchase can be a good deal, if you don't feel guilty about it. Or it can be a mess that has to be patched up before you can even consider moving in. There's almost certain to be stuff that the prior owners couldn't afford to fix, but hopefully your inspector will find most of that. Good luck!