First, are you sure you want to split your file? There are lots of things you will have to do twice; from resolving places to saving reports to duplicating sources and source media and other media.
What is the purpose of your desire to split your file? Is it so both you and your husband can work on the same file at the same time? Or, is it to export "trees" to give to cousins, or..???
If you going to do a straight export of descendants of an ancestor or ancestors of a person in your file - without regard to peripheral relatives - you can take a look at File > Export. This exports records and does not disturb your file.
To split a file, that is to export and then to delete people, you have to resort to the Charts in the Publish Workspace. The individuals in most charts can be exported and then deleted by right clicking in the blank area of a chart.
If you want to split your file into two pieces and keep peripheral relatives on both sides:
1) Make a duplicate backup file, with its accompanying media folder, in a separate folder from your main file and with a different name, to do the below steps.
2) Then, break the bond between you and your husband in some way. Either unattach yourselves as spouses, or unattach one of you from your parents.
3) Select one of you - husband or wife.
4) Now, go to the Publish Workspace > Charts > Extended Family Chart
a) UNCHECK the box to include ALL individuals.
b) Elect to include "everyone" related to the seleced person up to 99 generations.
c)Depending on the number of individuals, go get a large cup of coffee or watch some tv or go to bed.
d) Right click export everybody in this report.
e) In button bar - save this report.
I would save that report before deleting. I wouldn't delete these folks until I opened the new file and I knew everything was ok.
Then, re-open the saved file and right click delete the folks in that chart.
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This is the only way to include peripheral relatives in your report. Most of us accumulate parents of spouses, multiple spouses of parents and ourselves and siblings, etc. And, then accumulate children of those multiple spouses and so on. The Extended Family Chart is the only way in FTM to gather all of the periphjeral people in your file in one report. It gathers everyone connected to the selected person by blood or marriage.