Are there any additional costs if I share my mobile data with multiple devices via hotspot?

I'm with my 3 nieces in another house for 2 days because we're painting. The thing is, there's no Wi-Fi here, but they need internet for their laptops.

If I now buy data volume (24h unlimited) via mobile phone, do you think it would be possible to enable internet via hotspot 3 devices? Are there any additional costs?

If you have unlimited tariff it shouldn't cost more.