Hello Rob
As you thought, gooseberries do not come true from seed. They care
usually propogated from hardwood cuttings in the autumn. Usually
insert cutting, around 12-15ins, to half its length into a slit trench
by pushing spade into ground and rock to make trench, insert some grit
sand and insert cutting. Can be done in pots it only a few required,
but want a deep pot, like a rose pot.

As for your seedlings if you have the space - see what they turn out,
could have a good berry on your hands. As Peter said, is it a
seedling or is it suckering from the roots. Gooseberries are not
grafted so you can cut it down to its roots and pot on. If it is
suckering, you want to remove them, otherwise the bush will become too
dense and you will have mildew problems.

Good luck

Clifford
Bawtry, Doncaster, South Yorkshire