I differ from Ruby in that I wouldn't ask to see his place because it sends the message you don't trust him although you say you do. Is this a theme in your R? Have you thought that your mothering is better than his fathering? It happens, I think many of us think that at some time or another but it's not fair and it results in damaging your R with your H and his R with his kids. Just because we think something is "right" doesn't make it so.
Let your H develop his R with his boys, they're all coming to the age when a Dad is so important. And so what if they sleep on the floor, or wear the same clothes for 2 days or have hot dogs for dinner.
I was thinking the same thing. I really did impede my H's R with the kids. He now says, not really just that we are a good team, but I could/can back off alot. I know my H would have viewed me asking to see his apartment before/if I'd let the kids over as controlling and untrusting. The first time I layed eyes on it was when I dropped them off.
My suggestion would be to just call him and tell him they can stay there. You should definately drop off or pick up, but show some trust. Withholding the visit until you approve if the apartment does come off as not trusting his judgement.
M: 9 yrs T: 13 yrs H:34 Me:35, S4, D2, S 7 months Dday 11/12-PA & multiple PAs Dbing 12/12 S 1/13 7/13 H moved back in basement. 8/13 #3 born 10/13 still cheating 10/13 He moves across country, I file for D