Looking up the definition for expat, you get:
noun
noun: expatriate; plural noun: expatriates
ɪksˈpatrɪət,-ˈpeɪtrɪət,ɛks-/
1.
a person who lives outside their native country.
"American expatriates in London"
archaic
an exile.
synonyms: emigrant, non-native, émigré, migrant, economic migrant, guest worker; More
displaced person, refugee, exile;
Gastarbeiter;
informalexpat, DP
"the level of salary paid to expatriates working overseas"
antonyms: national
adjective
adjective: expatriate
ɪksˈpatrɪət,-ˈpeɪtrɪət,ɛks-/
1.
denoting or relating to a person living outside their native country.
"expatriate workers"
synonyms: emigrant, living abroad, working abroad, non-native, émigré; More
displaced, refugee, exiled;
informalexpat
"expatriate workers"
antonyms: native, indigenous
verb
verb: expatriate; 3rd person present: expatriates; past tense: expatriated; past participle: expatriated; gerund or present participle: expatriating
ɪksˈpatrɪeɪt,-ˈpeɪtrɪeɪt,ɛks-/
1.
send (a person or money) abroad.
"we expatriated the prisoners of war immediately after the end of the war"
synonyms: settle abroad, live abroad, relocate abroad More
So my suggestion:
We deal with problems uniquely facing those persons living, studying or working outside their native country
I specifically chose "uniquely" there to show that it needs to be for expats only - eg local tax issues affect everyone, not just expats, but inter-country non-residence tax issues affect expats.