No one can tell you what to do. Some questions to ask him
Has he done spay/neuters on small animals before? Is he going to follow the preferred anesthesia protocol? Have you talked to him and asked questions about the process of your babies' spay? What is he looking for on the pre-op blood work? etc etc. The more informed you are about the procedure and the more he can answer your questions, the more at ease you will be. Only you can decide if you are truly comfortable enough with him to have him do the procedure.
Don't be afraid to ask him questions, that might alleviate some of your fears. There are questions to ask in the stickys in this forum
PS, I agree, in the end, trust your instincts