Entering Bosnia, Croatia and Romania with a 2-entry Schengen visa

I'm planning a trip with my girlfriend who has an Indonesian passport and a Double-Entry Schengen Visa issued by the republic of Austria. We'd like to go from Austria via Hungary to Serbia and then via Bosnia to Croatia and back to Schengen (Slovenia).

Now there are some problems.

1. Going to Serbia is fine. Serbia lets Indonesians in with a stamp only.
2. But Bosnia probably not possible. Apparently we need a Mulit-Entry Schengen visa (called the embassy), they stated a double-entry is not enough. But I'm not willing to give up yet. Does anyone know if there is a chance to visit Bosnia? Visa is difficult as it's not possible to contact the consulate.
3. Croatia is slightly more complicated, but apparently we can get in as Croatia allows (Source):

All third-country nationals who are holders of valid Schengen documents[...] do not require an additional (Croatian) visa for Croatia.

Third-country nationals who are holders of:
uniform visa (C) for two or multiple entries, valid for all Schengen Area Member States; [...] do not require a visa for transit or intended stays in the territory of Croatia not exceeding 90 days in any 180-day period.

I'm just not sure if there is a difference if we enter from Serbia (having an invalid first visit already) or Slovenia (having it invalidated just at the Slovenian border).

4. Due to the problems with Bosnia the alternative route is to visit Timișoara in Romania instead of doing the tour in Bosnia and for Romania, which is like Croatia not part of Schengen I have even less information and at the embassy nobody ever picks up. I'm not sure if we are able to enter Romania from Serbia.

Has anyone of you ever had an experience like this and can advice me which part of the route is actually an option?