green card for parents of US Citizen - apply from abroad or from within US?

[Iepure Launtric]

I'm am a US citizen, my wife is a US citizen and we plan on sponsoring my mother and father who live in eastern Europe to apply for green cards. Is it better to start the application process while they are oversees, or is it better for them to come here (they have 10 year visitor visas) and apply here within the first 6 months of arrival. They've visited before for a few weeks. Never had any issues.

I'm wondering if the apply here... could they get denied the green card for some reason?

The whole plan is a little too complicated to get into but it all comes down to them selling most property back home and come live here. If they get denied the green card it would not be good for them with most property sold.

Generally what are the statistics when it comes to green card applications rejections?

Thank you so much.

[Enub4]

They should not travel to the USA with the intention to be permanent residents. If USCIS determines that when they entered the USA with a non-immigrant visa they had the intention to immigrate, they can deny the petition.

From what I read, the denial rate for parents of US citizens is low.