A picture tells a thousand words, as tne saying goes! I've never done these specific ones, but I see your problem, it's a balljoint. There is no special tool as such: the difficulty is caused by the fact that the nuts appear to be nylocs -a plastic collar inside the nut who's purpose is to prevent the nut coming undone in service.
This plastic collar grips the threads, and so this also makes it difficult to do the nut up because of course you can't hold the other side of a balljoint.......it looks from the pic that there's a hex head just above the rubber boot, which is what you need to get a grip on with a slim spanner while you tighten the nyloc.
Failing that, another option is to apply as much pressure as possible to the other side of the balljoint, and this type of thing can often be dealt with by fitting it with the car on stands, and then lowering it to the ground to load up the suspension, and then tightening the nuts.