Crapshoot,
Back in the midwest I loved squirrel hunting. Out here where we are, I really kind of miss them.
As to trapping them, they do learn to avoid danger, so having a selection of techniques to employ is preferable.
There is the old standby, the Havaheart type live trap. Wiring it open and getting the squirrels used to feeding from it is a good idea. Then, set it, deal with the catch, wire it open for a couple more days etc., etc. Having it be a sporadic hazard helps reduce trap shyness.
Set up a feeding station on the side of a tree ( I think I remember what a tree looks like). Wire a wooden pole or branch against the tree leading to the feeding station. Set some small baits on the pole as well. When they get to using the pole, wire on a bunch of small snares (if legal). Tree squirrels love to use branches to access trees and once the path is established, the snares do the rest. there is some danger of by-catch, but the set is pretty squirrel-specific
The next technique is more risky in that the potential for undesireable by-catches is increased. Also, an undesired target cannot be released unharmed. The use of big rat traps or tiny size Conibears can be employed in bucket or tunnel type sets. They actually do make tiny Conibear type traps smaller than a 110 that work on squirrels.
Legal issues need to be researched, but whatever technique is employed, results increase when the device is unarmed for period of acclimation feeding first.
Similar to your observations when we met out at the Silverton, traps work 24-7 whether your brother is there or not and are efficient. A good quality pellet rifle really turns it into an enjoyable experience though and is preferable ( My fave! ). Tell your brother they are also good eating!
Best Regards,
Sako