I don't know sqat about the MD laws in Romania, but to be safe, I'd ask someone on your father's side to make inquiry with the police (Politia de Patrimoniu) for their response; specifically MD-ing on one's own property. I doubt if it wil be an automatic "OK". This would include what permission or papers do you need to even bring in a MD.
Don......
Hey there mackaydon. Your answer is par-for-the-course when the question of ANY location comes up. Whether it be a type land in the USA, or another country , or ... whatever. The easy answer is: Ask. Who could argue with that ? I mean, .. .who better to know and ask, than the entity themselves, eh ? Therefore the answer rolls off the tongue.
Ask a border consulate, or a cop, or a city hall there, or a lawyer there, or an archaeologist there, etc... Right ?
Here's the problem: I'll bet you dollars to donuts that you will get a different answer from ANYONE you ask, simply depending on who you ask, how you phrase the question, and their mental perception of it. I mean, let's be dreadfully honest: We've seen this psychology over and over again at locations here: One person gets a "yes", another gets a "no", and ... meanwhile ... oldtimers who have never had any problems md'ing are scratching their heads saying "since when?".
And when it comes to finding some cultural heritage laws (that would *seem* to apply, and you've found a bored desk-jockey to point you to them), well gee: SO TOO does the same tend to happen here or anywhere. Some border lawyer cop or whoever points you to ARPA. Or to "disturb and alter". Or to "lost & found laws", blah blah IT'S NEVER ENDING. You can ALWAYS find a cop to tell you that you can't even pick your own nose or spit on sidewalks, etc...
So to the OP, I would turn the question around back on you: What did you "read on-line" that said it's illegal ? I'll bet you dollars to donuts it's a link to someone who fell victim to the very psychology I spelled out above. Ie.: they went and asked, and found someone to give their 'pressing question' a "safe answer". I may be wrong. Perhaps there is something specific that actually says "no metal detecting". If so, please provide the link you found. And even then: Be aware that whatever might sound "dire" might only apply to public land .
Why can't a farmer go look on his own land for the plow blade or wedding ring he just lost ? And also be aware that some laws in some countries that DO admittedly address border to border cultural heritage, often are just for ancient stuff. Same mindset of ARPA (where ours is 50 or 100 yrs.), yet in some of the European countries ... "old" is 500 yrs or more, blah blah .
I know someone who detected in Romania. But that was 20 to 25 yrs. ago. He found ancient coins. They detected on private farmer's fields with permission. They had no problems. Who knows? Perhaps they didn't ask enough questions of bored archies ? As to the reception they got with the locals and the farmers: They were well received. People loved to talk to Americans, were curious how it worked and what you found, etc.... Utterly no problems. That was not too long after the iron curtain fell. So perhaps this fascination with technology, and the admiration for western toys and culture is different now. I dunno.
Just go there and help those family members find that "wedding ring they just lost". Don't over-think it. JMHO