There are some words, and 'mayroon' is one of them, that need to combine with the connective (I'm used to calling it the 'linker', and you may see it called that sometimes). Sometimes the linker will attach right to 'mayroon':
Mayroong libro ang babae ('the woman has a book')
Tagalog also has what are sometimes called 'clitics', which are typically small words which like to attach, more or less, to the first word in the clause. And if you attach a clitic to 'mayroon', it goes before the linker:
Mayroon bang libro ang babae? ('does the woman have a book?')
Mayroon palang libro ang babae. ('oh, I see the woman has a book')
Mayroon pong libro ang babae. ('the woman has a book, sir/madam')
Most Tagalog pronouns are also clitics (all of the pronouns except for the ones starting with 'sa', and also 'ikaw'). So pronouns will also go between 'mayroon' and the linker:
Mayroon akong libro ('I have a book')
Mayroon kaming libro ('we have a book')
And that's what's going on in your sentence; 'kami' is attaching to 'mayroon' because 'kami' is a clitic, and then the linker (which 'mayroon' requires) is following 'kami'.
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