lettuce?

Can they have romaine and little gem lettuce? if so how much a week?

Romaine and Little Gem lettuce are fine for a rabbit to eat. Personally I would feed other types of green vegetable and forage though in addition, so that they have a variety. You should start off, like with any other new food, just giving a small amount and see how well the lettuce is tolerated. If there seems to be no problem, then possibly just feed a leaf every one or two days, but provide other greens as well.

Lettuce is OK to give to rabbits, but I would feed other veg that also has more fibre in it, as that is better for wearing the teeth down and for gut health. Don't forget they also need loads of grass / hay.

There's a lot of useful info here:

https://www.harcourt-brown.co.uk/articles/free-food-for-rabbits

thanks