I have a doubt about how to write "to be" in the following sentence:
Three movie showings to be (or to being) broadcast in next two months
Thanks for your help
Well, it's not a complete sentence, so that's not an easy question to answer. As a headline, 'to be' is possible, though the subject is more likely to be just 'two movies'. Movie showings are not normally broadcast.
If it's a contract, run it past a lawyer to check first. However, I would say something like Each movie can be broadcast up to a total of three times over the two months after the date of this contract. The sentence you have is too vague to me for a contract- you have to specify the period, that it is not three times a month for two months, etc.