is this normal ?

I'm not a lawyer but I would suggest for you to have the documents sent to you and reviewed by a local realty attorney before you sign. I would also suggest for you to retain a reputable lawyer in DR to ensure your best interest are looked after.
If he suggested he can rep both sides...That would be a red flag. He can technically but a reputable lawyer will advise you, first off, to get your own attorney.
Not to be long winded..Spend the few thousands it will take to be comfortable and do your homework. Make sure there are no judgments, or pending, against the seller or the land. They actually own the property etc...

Never give a power of attorney to anyone you don't trust 100 percent, and even then, avoid it if possible.

You can sign the papers yourself and have them notarized at your local Dominican Consulate. It will cost you a hundred bucks or so, a few days, and the time to drop off and pick up the papers, plus courier costs to get them to the DR, but worth it.

This is no reflection on the trustworthiness of your lawyer, and no reputable attorney will be offended if you insist on signing your own papers. If your lawyer takes offence, well, what more need be said.

We often act as POA for our clients in real estate purchases. The POA is very specific and only allows for the signing of the document of purchase AFTER the client has reviewed the contract both in Spanish and a legal English translation. Then after wrtiten apporval from the client are the documents signed. The POA then immedialtly expires. If you have other questions please feel free to PM me.

Bob K