My family is using Adverse Possession to obtain a piece of property, after a year we are informed that we have to leave the property by 5/4/08 or be arrested for trespassing. Can we be arrested??

Yes if they say you are trespassing then you can be arrested.
To do adverse possession you can not have anybody protest your being there.

First of course as you found out, adverse prossession is seldom allowed, the rules are sto stict as to what is required,

So we will not rekindle that since you have found that out.

But yes, if the court has ordered you off by a certain date you can be arrested, normally what they do is come out like in an eviction and have you leave the property and sit your belongings to the curb.

Then if you return they arrest you for criminal tresspass. BUT>>>> since you have had a formal warning yes they can arrest you if you are not out

And since you tried to take ownership from them, I am sure they will push the police to the full extent of the law.

My family is using Adverse Possesion to obtain a piece of property, after a year we are informed that we have to leave the property by 5/4/08 or be arrested for trespassing. Can we be arrested???
In a word - yes.