On grammar

khoshtipIs it correct to replace the word "be" with "have" in the following sentence?The shapes must be the same size.

You could.

khoshtipWhat is the role/effect of the auxiliary verb "does" in the sentence below? Emphasizing?He does speak to them.

Yes, it's for emphasis.

teechrYou could.

What about this one:
The shapes must be in the same size. Or, they must be in same sizes.

teechrYes, it's for emphasis.

Can we say in any situation, when the auxiliary verbs do, does and did have come before the main verb, they are for emphasis?

khoshtipThe shapes must be in the same size.

No.

khoshtipthey must be in same sizes.

No.

khoshtipCan we say in any situation, when the auxiliary verbs do, does and did have come before the main verb, they are for emphasis?

In positive sentences, that's usually the case.

Thank you.

You're welcome.

You are the only instructor that responds to a thanksgiving message.

khoshtip You are the only instructor that responds to a thank-you thanksgiving message.

Note that Thanksgiving is a major annual holiday in North America.

Yes, but the dictionary mentioned both, anyway.