I was thinking that maybe lunch was winding them up. What about trying something low in carbohidrates like veggies or fruit or even cereal? staying away from cheese, yoghurt an that kind of treats might help them relax sooner.
If they don't get that nap time = quiet time = crib time alone in their cribs, then a few sessions of walk in walk out would be recommended. That also depends on child's temperament cause they can also find the wi/wo as a peekaboo session since they are reluctanct to go to bed.
Another thing that comes to my mind is a longer wind down. Long as 30 mins, starting waving bye bye to things at the house (we even say night night to the vacumm and blender lately
). I found that i had to "convince" ds that he had to start relaxing by letting him now it was nap time FOR EVERYONE IN THE WORLD LOL... so we spend a good 15 mins bye byeing things, then we tide up his room to prepare it for sleep, he helps me make bottle, put on pj's, etc... The more we associate things with bedtime, the more he's likely to go down without much fuss. Then i give him bottle, sing a few songs, tell him i love him a lot and that i'm tired and need to go to bed myself (oh dear God how i wish this was true LOL). When he had his nap strikes, i would leave the room the same and he'd protest and cry so that's when the wi/wo thing started. Even now somedays i hear him crashing the room, singing, talking for 20 mins and i start to freak out but i leave him be as long as he's not crying. He cries, i do wi/wo... and to my surprise when he's singing super loud the next minute he's out.
Then when you've done all this and they still won't nap...well, there's no much you can do except for being consistant with the timings, routines and methods and hope for the best. You can provide the oportunities for sleep, help them go to sleep but unfortunately, can't make them sleep.
HTH! and i sure hope this is just a week off for the sleep of your lo's!!!!!!!!!!