It is better to change it to "a XXX method and its device"
2. The point is, can the name contain the words "and", "and" or "?
All three words can be used casually, as long as they conform to the provisions of the patent name. If (diapers for the elderly or children) are correct, if (diapers or long pants) are wrong.
3. From another point of view, can a patent only "contain" an invention content, and must different contents be applied separately?
For example, in an invention, there are both methods and actual device design.
Compliance can be regarded as a patent application, and only the patent fee is paid.
Please refer to Chapter 6, Part II of the Review Guide for the relevant regulations on singles.
4. Besides, there are three design methods to realize it. Can it be clearly stated in one patent, or must it be separated into three embodiments or six documents?
Three design methods can be written as three implementations in a patent application.