Long term Coquelin could be a good right back, but short term he's a liability. Great going forward, but so much to learn tactically and positionally.
Yennaris is much less likely to cost us, he understands the position much better, but doesn't have some of Coquelin's attacking qualities. If he can cope with the pressure of it all, and the jump in the physical qualities of his opponents, then I think he could do well. I really like the calmness he has in all situations. No rash tackles or crazy decisions, and that calmness shows in his passing also.
Jenkinson isn't ready for me. Shouldn't be a factor.