S4-R1: I normally would say that whenever one has 2 trump + 2 aces and they don't block all suits they should call. However, S4 does block 2 out of 3 suits and he traps a Next call nicely. Given how aggressive S1 is, I cannot say S4's pass is wrong. It's another hand that needs to be tested and I wouldn't be surprised if passing beat out calling.
S1-R2: Standard spade call with R+1+A but S1 has to believe in it. With an off ace to promote, lead the Right.
S2-R2: After S1 leads garbage (TC), S2 controversially does not trump in with just a single Ace of trump. Instead he throws off short-suiting himself in diamonds (QD). Keeping the Ace of trump behind the maker does maximize euchres but this strategy obviously can backfire.
S3-R2: S3 wins the first trick by trumping in and he has the Left in trump left. Should he lead it? The answer is yes. When S1 jumps the fence and leads garbage, he will have either R+1 or R+2 with no off aces. Either hand would LOVE to see the Left led. Also in this spot, before trump has been led, the turned down suit (diamonds) is the worst possible lead, and it's even worse in this spot given that S2 threw off a diamond on the opening lead. The best lead here is the Left, the 2nd best lead is a heart (QH).