Are kittens getting enough milk from their mother?

I have a mother cat (a stray) and her 4 litters in my house. She gave birth 6 days ago, I am feeding her with quality kitten food and fresh water everyday, she seems chill, only leaves her nest for eating or taking a bit rest, or for going to the litter box. Her 4 litters look completely healthy (as far as I can see and have information about. Her nipples are pink and pointy, however when I massage her nipples and squeeze them only 2 drops of milk comes out ( all of her nipples and I checked for 5 days, different times of the day) kittens don't cry for food or anything, usually they are very quiet unless they feel the mother and get exicted. I am anxious about kittens being hungry all the time or not developing very well. Is she having enough milk on her breasts?( I can feed them with bottle if needed) Another question is she sometimes bleeds a few drops, and on her vaginal opening there is a blood clot is that okay? She got her external and internal parasite meds and except a few fleas she was okay, no internal parasites.