Don't write the same way as you would for an English or regular History essay. Break the question up into different sections. Highlight the key parts of the questions, eg techniques used, style, artists that were influenced, composition etc etc and make them into titles. Then under each title write about your named paintings in relation to the title. Have an intro and conclusion as well. You can reference other paintings as well but as long as you're constantly referring back to the question asked and not leaving any part of the question out you should be fine.
My teacher always told us if we arent great at writng in an essay format, don't. Once you have all the relevant points theyre looking for included you will get the marks for them. You can simply highlight the parts of the question and answer each part in a series of hedings with the relevant points underneath to form some sort of a paragraph. It's not an english essay so it wont be corrected like one, all you have to make sure is that you get the information down