update validation for non joint purchase

app/models/form/sales/questions/number_of_others_in_property.rb

@@ -8,6 +8,6 @@ class Form::Sales::Questions::NumberOfOthersInProperty < ::Form::Question
     @hint_text = "You can provide details for a maximum of #{joint_purchase ? '4' : '5'} other people."
     @width = 2
     @min = 0
-    @max = 4
+    @max = joint_purchase ? 4 : 5
   end
 end

spec/models/form/sales/questions/number_of_others_in_property_spec.rb

@@ -36,11 +36,23 @@ RSpec.describe Form::Sales::Questions::NumberOfOthersInProperty, type: :model do
     expect(question.hint_text).to eq("You can provide details for a maximum of 4 other people.")
   end
 
+  it "has the correct min" do
+    expect(question.min).to eq(0)
+  end
+
+  it "has the correct max" do
+    expect(question.max).to eq(4)
+  end
+
   context "with non joint purchase" do
     let(:joint_purchase) { false }
 
     it "has the correct hint" do
       expect(question.hint_text).to eq("You can provide details for a maximum of 5 other people.")
     end
+
+    it "has the correct max" do
+      expect(question.max).to eq(5)
+    end
   end
 end