Pregnant, due in February and still breastfeeding 15 month old

How do you go about feeding both babies? I’m all for feeding as long as I can for my first but what about tandem feeding? I don’t have anyone in family that has breastfed two babies at once at different ages. My son feeds a few times a day for a bit but refuses breast milk from a cup or bottle...unless I put a little bit of chocolate milk in it but still prefers me. I don’t want to wean him but I don’t want my first to feel upset or jealous. Any advice?