That sounds like typical behaviour for new fish. Shoaling fish swim together when they are threatened. Being caught in a net, put into a bag, then put into a tank that looks different with slightly different water and less of them is threatening to a fish. They respond by schooling.
I got 7 Danio tinwini on Saturday, I think I have 4 males, 3 females. One of the females has taken over a hollow plastic root ornament and chases the other danios out. Shoaling fish often 'do their own thing'. Shoaling is not the same as schooling
The only way to find number 10 would be to completely empty the tank, which is not a good idea as it would stress the fish even more. It is OK to very gently lift up ornaments or shake plants but not so much that you scare the fish. Check inside the filter too. With the Juwel one, it is not unkown for small fish to squeeze though the tiny gap between the casing and the outlet tube. And check the floor at the back of the tank as it is possible for them to jump out through those cut-outs at the back. I've never had a fish get out through them, but I have had fish jump out of other tanks.
Give them their first feed today, but only a small amount at first. Wait till the light has been on long enough for them to wake up. Watch them after the food goes in (but I can't think of anyone who wouldn't with new fish
) and see if they eat it. New fish quite commonly do not eat when you first get them. It could be something as simple as using a food different from what the shop fed so they don't realise it is food. Clean up any uneaten food after a few hours, and persevere. It won't take them many days to start eating.
If you have flake food and the flakes are quite big compared to the size of the fish, crush them up a bit before dropping them in the tank.