My husband was assigned a guardian, and in the last 7 years they've gone through his estate. How can I file an appeal?

A lot more info is needed.
According to the profile his primary problem is mobility.
If he is "of sound mind" why did / does he need a Guardian?
And who are "they"

Yes, in some places the county guardian can do whatever they want. Spend all of the money, sell the house, ban the family, etc. It happened here in Las Vegas. They can do this but in at least one case, which is still in court, the guardian and the judge involved in it are out of that position and are awaiting trial for their actions.
Oh, and when the family took this to court, the guardian spent
persons money to defend him against the family.
Who to contact? I would try every agency and law firm in the state. The internet can be very helpful in this.

You need to give A LOT more information. Who are 'they'? Who is doing all this? How can they isolate your hubby from you and ban you from seeing him? Nobody can halp you unless you give some more information, sorry.