Help with DW Schema queries

Use this (I can't see you passing Database here. You might need to replace Database with something like "Database" here depending upon your database name)

let
    fxConnection =
        (server as text) as table =>
            Table.AddColumn(
                Sql.Database(server, Database){[Schema="DW",Item="DEClass"]}[Data],
                "Server",
                each server
            ),
    #"CombinedTables" =
        Table.Combine(List.RemoveNulls(
            {
                if ACT_SourceARA = 1 then
                    fxConnection(ARA)
                else
                    null,
                if ACT_SourceGOI = 1 then
                    fxConnection(GOI)
                else
                    null,
                if ACT_SourceIBI = 1 then
                    fxConnection(IBI)
                else
                    null
            })
        )
in
    #"CombinedTables"