TIFU - raw chicken

So, somewhat as the title says: I fucked up the Christmas chicken.

I was making two whole birds, about 1-½ kg each. Inside of each, I put ¼ of a lemon, half a head of garlic (about 8 cloves), a small (whole) sweet onion, fresh rosemary and some compound butter. I put the two birds side by each in the roasting pan, uncovered, at 390F (200C). Directions I’d found said, at that temperature, should take about 20 minutes / 500g + 20 minutes. So I figured 1-½ kg bird, should take about 1 hr 20 min - 1 hr 30 min. I cooked them for near 2 hrs because my mother in law insisted on putting two casserole dishes in the oven with the birds which fucks up everything. After all that, the breasts were beautiful but the legs and wings were fucking raw.

Christmas dinner. I was able to save it, but all the timings were shot, some of the meat ended up dry, and it’s just not how I wanted this to go. I’m fucking pissed off at myself.

I figure there are three things that could have fucked this up. I might have over-stuffed the birds (those onions should have been mush but they were still quite firm). I might have needed longer because there were two birds. Or mother in law’s casseroles could be the culprit, impeding the air flow. Or a combination.

Anyway, this was a maddening and fucking embarrassing experience and I’d like to not repeat it.

Opinions on how I fucked this up? Tips on how to not fuck it up again?

Thanks.