I would try to keep bfing. It is possible, and safe during a normal pregnacy, to continue to bf another baby while pg. Your supply should actually increase, to start preparing for the new baby. Keep up your fluids, be sure to drink lots of water, and pump inbetween. I would also work on getting your 6 mo to take a bottle (not sure if it is the bottle he doesn't like, or just the formula). If he takes Bmilk from a bottle well, I would slow add formula to it, 1/2 oz at a time, slowly over a few weeks, until it is all formula. You may need to try different bottles/nipples, or different formula. If he takes Bmilk well from a bottle, he should eventually take formula well. If he is on solid foods already, I would push more of them during this transition. You can also try a cup (with formula, water, bmilk, even watered down juice) to see if he takes that better. Congrats on the new baby, and on the choice to breastfeed.
S., mom to 3 (all who were bfed)