Help on vacation – tires broken?

Hi I’m trying to be brief but I really need help. I have no idea of cars, let alone of the tyres. I’m on vacation with the car on the North Sea. Just before the trip started I checked and filled up the tyre pressure of my ups (were missing 0.1-0.3 bar for all four tyres). Yesterday evening after 5 days a lot drive, the alarm showed that the tyre pressure was not right anymore. So I down at the next tank and checked. 3 all right. Only number 4 (back right) showed only 0.9. I inflated him without thinking big on the given 2,1 again and drove 60km further. I arrived at the hotel then still once Googleled and get it now totally with the fear to do. Then then this morning again checked and he was again only on 1,2. Now I sit in the ship to Helgoland and eigtl should go tomorrow with full packed trunk again over the highway home. Tonight and tomorrow the car Werkst had been closed here and I don’t know what to do now, have just really shot to drive the car home so, is not in it. But must also tonight 3km from the harbour into the house zzrück. What should I do I really have no idea about that. Maybe I should mention that I hit a high curb with this rear wheel 2 weeks ago when I turned right into a road, but you could not see any visible damage and since then have also I didn’t see or see any damage or any other damage that he looked flat. The tire looked full. Also, the car doesn’t pull out of the track or jerks in any way. Am really stunned what I should do?