For realistic paintings like this, you really do have to shoot adequate photo references to work from–you can’t guess or fake anything, and you can’t just piece together references from various other sources because they are in totally different contexts and won’t form a cohesive, organic whole.
My suggestion is for you to take your camera, tripod, and ask your friends and family to pose for you. Use yourself and a large mirror if you need to. Use household lights to light your models, and direct them like a movie director would to get the right expression/pose you need. Rent costumes from costume shops of you need to, including the suit of armor.
Also, don’t just slap the figures in front of a background–think about the narrative, the premise, the location, and the whole scene like a movie set, with background and props like a real living space.