How to select a value depending on 2 attributes from separate nodes using XPath in C#?

Question

So, I have an XML file like the following structure,

<Root>
  <Parent StoreDate="2014-12-31" Type="1">
    <Child1>2014-01-31</Child1>
    <Child2 TimePeriod="M1">
      <GrandChild1>-4.58849</GrandChild1>
      <GrandChild2>288</GrandChild2>
    </Child2>
  </Parent>
  <Parent StoreDate="2014-12-31" Type="1">
    <Child1>2014-02-28</Child1>
    <Child2 TimePeriod="M1">
      <GrandChild1>4.58015</GrandChild1>
      <GrandChild2>284</GrandChild2>
    </Child2>
  </Parent>
  <Parent StoreDate="2014-12-31" Type="1">
    <Child1>2014-03-31</Child1>
    <Child2 TimePeriod="M4">
      <GrandChild1>-0.65693</GrandChild1>
      <GrandChild2>284</GrandChild2>
    </Child2>
  </Parent>
  <Parent StoreDate="2014-12-31" Type="3">
    <Child1>2014-03-31</Child1>
    <Child2 TimePeriod="M1">
      <GrandChild1>-5.65693</GrandChild1>
      <GrandChild2>2334</GrandChild2>
    </Child2>
  </Parent>
</Root>

I want to select all GrandChild1, if attribute [@Type] of Parent is 1 and attribute [@TimePeriod] of Child2 is M1.

I've loaded root in an XElement named xElement. Then, I'm using

IEnumerable<XElement> elements = xElement.XPathSelectElements("(/Parent[@Type='1'] | /Parent[Child2/@TimePeriod='M1'])/Child2/GrandChild1");

This supposed to select only the 1st and 2nd GrandChild1 from the above XML file. Instead it is selecting all GrandChild1. What am I doing wrong?

I've tried using 'and' instead of '|' in the code. But it's not working at all and throwing exception.

Any suggestions guys? Thanks in advance.

EDIT:

I also want to select Child1 with the same condition. What do I need to do?

Answer 1

EDIT: Adding code to select Child1 after the question was changed.

Code to select Grand Child1 You can use //Parent[@Type='1']/Child2[@TimePeriod='M1']/GrandChild1

Child 1 Selection XPath: (One way to do)

//Parent[@Type='1']/Child2[@TimePeriod='M1']/../Child1