About an Agreement.I like to tell in the beginning.I am marriage a filipina 1994,now i have big problem this?

I give money to my wife in 1995 to buy a lot,and after 3 yrs.i make a house 750sq.meters only.but when i am coming back to philippines i see beside my house a small house.I wonder why because that is not my plan,I ask my wife,she tells me that her sister living there because when we going in europe they look our house,same care taker.Then I said,ok.only for looking.But in 2001 the relationship between my wife and her sister was not more good.Because my wife looking for other people can work,now new people work,the niece and brother(young).But sad to say my wife sick in germany and cannot more helping the doctor,only a months in hospital from liver cancer and was died 2005.Now begin my problem,We have 11yr.old son,now our lot the tax declaration have problem,AGREEMENT between the sister of my late wife that they can live in the small house until they like self abandonment.But cannot damage the house always maintaining it,in the Agreement write must let the owner know the lot if have things to do.But they destroy my fenced make small way going to the son of these family.But this Agreement i not knowledge this,beginning 2001 july.but they Annotate 2009,i know these problem only last 2009.THese written agreement i saw my late wife signature on it.i not know all about this situation,this documents.Problem in philippines the white men always loser,how can away this problem where these couple lives like much money,I also like know what case i have to fight.I see in deed of sale,1995 buy the lot,but not the house,but it was lie,in 1994 no house,yet.only 1998 begin.