HTML5 doesn’t restrict how many meta elements you may have.
We can never know for sure what specific consumers (like search engines) would like to see or how they handle it (and discussing this is off-topic on Stack Overflow), but there is no reason to assume that they’d have a problem with this.

In HTML5 you may only use metadata names that are defined or registered.
You’ll see that subject is not a valid metadata name.

In your specific example, you could omit one meta element, as you are using RDFa for og:title, and you can have a metadata name (in name) and an RDFa property (in property) on the same meta element:

<meta name="twitter:title" property="og:title" content="post-title">

HTML5 doesn’t restrict how many meta elements you may have.
We can never know for sure what specific consumers (like search engines) would like to see or how they handle it (and discussing this is off-topic on Stack Overflow), but there is no reason to assume that they’d have a problem with this.

In HTML5 you may only use metadata names that are defined or registered.
You’ll see that subject is not a valid metadata name.

In your specific example, you could omit one meta element, as you are using RDFa for og:title, and you can have a metadata name (in name) and an RDFa property (in property) on the same meta element:

<meta name="twitter:title" property="og:title" content="post-title">