This more than likely will sound really direct.
Why are you forcing her to do something because you want it? You stated she has hesitations. Now we do not know what the hesitations are, and you may not know all of them, but do you OWN her? Shouldn't she be able to do as she pleases with her life and have you along for the ride?
Here, let me try this a different way. Wanna take a quick poll? Ask 100 women in the lifestyle if they think two guys giving each other blowjobs is hot and you will probably get about 70% that think it is hot and want to see it. Would you like your wife to come on the forums and say, "Husband's first cock sucking I want my husband to suck a cock and take a load in his mouth. He has hesitations. How do you progress into this?"
Now of course, if you are bi, dammit, my rant makes no sense :)
In my opinion, part of the lifestyle is about being able to comfortably discuss your desires/kinks with your spouse and then being able to execute it. So if you have no desire to execute her desire for you to take a load of cum in your mouth, that ends it :)