I want to make a master layout for invoices and receipts which will include a company logo and signature of authorized person in (png/jpeg format).
So what should be or what is the standard size for brand logo and signature?
There simply isn't a standard size
I know it's not the answer you want to hear, but it is the answer to this question.
One company might adopt a standard size, but that will be because that standard size worked for them dependent upon the layout and design of their invoices, the legibility and aesthetics of the logo at various sizes, and lots of other factors. The fact remains, there is no global standard.
EDIT: I think it's worth pointing out (re @Digital Lightcraft comment) that of course if a particular company has developed a style guide then of course that will dictate the size of these things, so in that instance there will be a standard, but of course only for that specific company, and not, as OP was suggesting, globally.
Each branding project comes with its own standard, which yourself or others are setting. So whatever works i guess. Make your logo 5cm wide and print the template. If you can't read it, make it bigger until it looks right. And that you can then call "standard".
In my company the standard is 600x116px, but as "Lightcraft" said there isn't a standard for everyone; it depends on the companies own guidelines.