Please ..Help I need Advise Asap!!

So i am ready to have sex iam 18 and my boyfriend just turned 21 (we are legal) my grandparents raised me and they are old fashion meaning the pressure me and my boyfriend to have sex after marriage and also im scared that i will disappoint them because they have high expectations for me which i hate ...but i don't want to wait.. me and my boyfriend do sexual things ALOT but never intercourse i do not know how to tell them im ready to have sex me and him are both ready.What should I do??