With option multiple you can test nested models under the first model. We provide a few nested in a certain order. Feel free to change the order of the option multiples, and add other tests that you think are important.
Sometimes you may find that the order in which you choose to test nested models affects the results you will get. This may be due to a lack of statistical power. For example, if you choose to test whether there is a difference in means between MZ and DZ twins, after you have tested for an effect of first or second born twins, you may find that the difference between MZ and DZ twins is statistically significant. However, if you would have tested whether a firstborn MZ twin differs from a first born DZ twin and a second born MZ twin differs from a second born DZ twin, you may have not find a significant effect of zygosity. This may be because pooling across birth order may give you just enough statistical power to detect an effect of zygosity, or there may be interaction effects of zygosity x birth order in your data.
Sometimes, if you are a purist and follow all options, it can be really difficult to decide what effects are at play. It is always wise to decide beforehand what is really interesting and let that guide the sequence of testing.
When writing a paper it is a courtesy to the reader to provide the fully saturated descriptives as well as the statistics from the best fitting model. Describe in the text what the sequence of testing assumptions has been.