I think the issue here lies in that you are attempting to match frequencies based on two variables that are not formulated using the same methodology/are not available for the same samples. See my notes here on the differences between the two.
Here is an example of Stata code, which relies on examining relationships to the head of the household only, that you could use to determine same-sex couples using SPLOC and RELATE (you will need to attach spouse characteristics for SEX – sex_sp and RELATED – related_sp when creating your extract):
keep if pernum == 1
keep if sex == sex_sp
keep if related_sp == 0201 | related == 1114
Because SPLOC and SSMC are created in different ways, considering just same-sex married couples, you will end up with two different values depending on your approach. Which approach you use is ultimately up to you and will likely depend on the scope of your analysis.
I hope this helps.