I hae never done the trap part of trap - neuter - release. However, since this appears to be a family, it occurred to me that keeping some fur brushings from the first ones you catch may be useful in the trap to catch the later ones. Assuming you can get anywhere close to them to run a brush over them! Maybe while they are "out" during the spay / neuter someone can run a brush over them for you! Just a thought. Godd luck getting ALL of them!