Also have them watch you, if comfortable of course. It also might be easier to focus on one at a time. Or do the girls together and then your boy or however. You do the girls dad assist with son. Reusable bed pads on sitting surfaces will be helpful.
No advice. My boys are 15mo. Just sending all the good vibes and prayers mama!
Are they all ready? Showing signs of interest? Can they each get on the potty themselves or do they need help. I would use a step stool, reward chart a timer and stickers. A special treat after staying dry for however many days. Have them pick out favorite underwear and only do pull up/ diaper at night. Give them a lot of water during the day so their bladders can feel the sensation of being full and cut off liquids an hour before bed. Only small sips of water. Have them use the potty first thing in the morning and 20-30 minutes after liquids and before bed.