Okay so first.. as reference we have seen Silva and Zeno fought againts Kuroro. Zeno actually said that if Kuroro fought seriously that the Zoldycks might lose. Plus.. Silva have fought againts Kuroro in the past and based on their fight he warned Killua to not cross fist with Ryodan, although we never know the result of their fight but it seems like Silva very impressed with Kuroro. So it's clear that Kuroro is stronger than Silva and Zeno. But watching current ability of Silva and Zeno in chimera ant arc i do believe they have the skills needed to be on par with Kuroro, or even beat him, i mean.. Kurapika capable to captured Kuroro, i believe seasoned assasins like Zeno and Silva could do something to get the upperhand
But hey.. this is not just three of them, it's a group fight so we might consider how the other perfoms while Zeno and Silva pinned Kuroro down. For this thing i'd like to assumed that Ilumi is on par with Hisoka in term of fighting skills, so the question is : how good Hisoka if he fight the members of Ryodan? The answer is we don't know. But Hisoka met with Ryodan member in Greed Island once, and he surely looks confident, didn't afraid with the possibility of fighting them. Oh and he also catch Machi with no difficulty in heaven arena. So i believe Ilumi is also capable to fight several members of Ryodan, of course with help from Killua
The wild card from this fight would be Maha Zoldyck. Nothing known about him at all, he could be very strong or very weak because old age. It would be trouble for Ryodan if Maha is strong, he can change the battle flow with him fighting Kuroro, making Zeno and Silva free to help Ilumi and Killua againts the likes of Uvogin, Feitan, Phinks, Nobunaga and Franklin
Now about Kikyo, there's also no info about her fighting skills but being Silva's wife i think she's also capable fighter, he could be a match for Machi and Shizuku, or maybe not..
Meanwhile Milluki, Kalluto, Pakunoda and Kortopi would be among the ones to fall first, and maybe Alluka too, but about Alluka.. his power is terrifying, he's capable to kill the Ryodan, but that only happens if he can utilized his power, but can he utilize his power in the middle of the fight? Too many uncertainty just like Maha Zoldyck
Okay so to make this short.. Ryodan win because of their number