Just a couple of tips
Yugoslavia has not existed for at least 5 years now.
Not all names from the area end with IC, this is a common belief but not true. Many names in Croatia end with OV, which is a diminutive, IE STEFANOV would be son of Stefan or little Stefan. However after looking for Canadian immigration records I believe you are correct in the spelling being STEFANOVIC.
The correct spelling is Dusan (sounds like dooshon) Lucy could be Lucija or Luca. Dusan is correctly spelled on a Canadian Border Crossing document for Steve from 1923 when he is going to Ohio. But he is listing Hamilton not Regina as his father's residence, which would make more sense as to this day Hamilton (with its steel mills has a large Croatian population) His Certificate of Arrival for his US Citizenship shows this as his entry into the US. The place of birth listed is Varkazdin Yugoslavia for both Dusan and Steve, this place is most likely Farkazdin located in Serbia about 25 mile n. of the capital of Belgrade. http://atlas.mapquest.com/maps/map.adp?searchtype=address&am...
Also Dusan's wife is listed on his Citizenship papers as Ljubica which translates to Violet not Lucy. Children listed are Steve, Joseph, Anna and Eva. Farkazdin is located in what had been the Kingdom of Hungary until after WW I, the region was known as the Banat, maybe that is where you are getting that he was born at Benot?
As far as living relatives in Serbia, STEFANOVIC would be a very common name so it is difficult to say.
I am having issues finding Mary OSTERICH... in Croatia I do not find this spelling rather I find OSTARIC (the C has a diacritic which makes it sound like CH)... and Mary could have been Mara, Marica or Marija. But if you look at the 1930 census there is a notation that she arrived in the US 1914 and was already a Naturalized US Citizen... looking at Naturalization records I find a Certificate of Arrival for Summit Co Naturalizations for Maria OSTOJIC arr 1914 aboard the infamous Lusitania This must be her because her record is cross referenced to Mary STEFANOV! She arrives in 1914 with mother Kata former residence and birthplace Borovitz destination to husband/father Stevo at Conway PA Stevo is listed as coming from Borovac as are some other OSTOJIC arrivals Borovac is near Nova Gradiska Croatia and there are some OSTOJIC phone listings in towns nearby.
As a backup to this OSOJIC info I find a 1920 census for Conway PA listing showing sibling names you mentioned.
Steve Ostrich 40
Katy Ostrich 35
Mary Ostrich 10
Helan Ostrich 5
Pete Ostrich 1 6/12
As far as finding relatives this may be able to be accomplished but you first need to establish your facts abou your family history. Looking in the Serbia online phone book for Zrenjanin, where Farkazdin is located, finds 53 phone listings none in Farazdin proper but some in nearby Centa and other places.
Link to Serbia phone book NOTE to search Serbia phone book you must use the letters with diacritics such as STEFANOVIĆ note the mark over the C you can simply copy and paste this into the phone bookhttp://www.belestrane.nadlanu.com/site/default.asp?lang=en
OSTOJIC has over 800 listings in the Croatia phone book with 50 in Slavonski Brod Posavina County.http://www.tportal.hr/imenik/default.asp?lang=1
If you like you can contact me direct at firstname.lastname@example.org
Croatian Heritage Museum