”If you have Finnish ancestry or a close connection with Finland, you may be granted a residence permit in Finland on this basis. This means that you are considered a returnee (paluumuuttaja). Receiving a residence permit depends on the directness and closeness of your Finnish ancestry. No other reason, such as work or study, is required in order to receive the permit.”
Not an expert but I would imagine grandparents is considered pretty close and direct.
https://www.infofinland.fi/en/moving-to-finland/non-eu-citizens/remigration-to-finland
”If you have Finnish ancestry or a close connection with Finland, you may be granted a residence permit in Finland on this basis. This means that you are considered a returnee (paluumuuttaja). Receiving a residence permit depends on the directness and closeness of your Finnish ancestry. No other reason, such as work or study, is required in order to receive the permit.”
Not an expert but I would imagine grandparents is considered pretty close and direct.