"The labelling AV1, Av2 etc is just a way to distinguish between different sockets on the same box - it can be other types of sockets too, not just scart sockets, which are labelled AV something. There's no magic in the numbering - AV1 could be an output on one box, but an input on another; AV1 could be a scart socket, AV3 composite video etc - you just have to check the manual to find out...."
if your tv has only got one scart socket you can daisy chain scart devices so all can play through that one socket.
for example, you have a dvd player and a sky box that both have 2 scart sockets on them you can connect the dvd player to the TV scart and then connect the sky box to the 2nd scart on the DVD then the TV will display the picture from whichever one is switched on