Instead of 2 tsp of lemon extract how much juice from a real lemon should i use

You probably don't need to add the juice. For a cake the size of a loaf, I use the zest of a whole lemon (or 1 tablespoon as my recipe states) ; if you are making a larger cake, you can probably increase this. When it comes out of the oven, poke holes with a toothpick and drizzle with a mixture of freshly-squeezed lemon juice mixed with sugar--delicious. Again for a loaf cake, I use 1/4 cup freshly squeezed and strained lemon juice and 1/3 cup sugar (for a more tart flavor I sometimes switch the ratios and use 1/3 cup juice to 1/4 cup sugar but I love tart flavors). Stir before pouring over the still- hot cake. For a ring cake or bundt increase accordingly. The ratios of lemon and sugar (above) are for a loaf-cake but make a generous amount of drizzle. For the loaf cake I cool 10 minutes on a rack then turn it out on the oiled rack (then flip it to cool right-side up). I haven't made this in a bundt, and understand cooling and turning out is more challenging, so for cooling and turning out advice, I defer to the bundt experts.

I would use 1 tbsp. lemon juice and the grated entire rind of the lemon. The lemon flavor is largely in the lemon oil in the peel.

I would use the zest of 2-3 lemons and maybe a teaspoon of juice. Lemon juice is very acidic, and too much will change the texture of your cake. (I know this from hard experience.)