Physics has a reputation of being extremely difficult, and that you have to be a maths wizard to study it, but you really don't. The majority of the maths in Physics is just substituting values into formulae that are given to you in the log tables, so you don't even have to learn them off. Then you just manipulate the formula around to evaluate the desired variable. The particularly hard aspect of Physics is learning the definitions. Each definition is extremely specific and pretty much must be learned off word for word, as leaving out one part of the definition could give off a completely different meaning.
As for biology, like I said, there is a lot of theory. There are 41 full chapters in the Leaving Cert Biology book by Michael O'Callaghan, each with its own unique set of theory, definitions, diagrams to learn, etc. Biology is definition a subject that you have to really work hard at from day one of 5th year, and you'll have no trouble if you do. However, section A of the Biology exam paper is usually easy. There are just short, one worded answers that you've to give, and they give you a diagram where you have to label some of the parts, things like that.
I am currently taking biology, chemistry and physics. I'm not the best in school and tend to take longer to do or learn things than my classmates. There is a fair bit in these subjects, and lots of people seem to think it's crazy to do all three. But realistically if these are the subjects that you are interested in, you will be better just doing them all rather than something maybe easier, but that you don't like as much. Saying that, I don't think there are any 'easy' LC subjects, they all have their own elements in them, so its really based on what clicks for you and what you enjoy most. And if these are useful subjects for college courses you're interested in all the better.