I say let the weekest link go, whether it is the newest guy or not. If it is someone other than the newest guy, it will show the others that their job is not as secure as they think and that the need to prove their worthiness. Do the math out and see what your costs are, is it cheaper to pay for the extra employee for 40hrs or is it cheaper to pay all of the guys 10-15hrs of overtime. If they are all getting payed the same, then it would be cheaper to pay for the 5h guy. Depending on what you pay foor benefits, it can change greatly.
Also, were coming up on the fall cleanup season soon. If your 4 guys are working overtime now, they will be even busy in a couple months.
Why do people not respect us as they do other tradesmen? Because every Tom, Dick, and Harry doesn't think he can be a plumber or electrician!