Take the lobsters and be sure to clean any black parts by removing them to avoid bitterness. Then cut the legs off and cut then up. The bodies should be cut up as well to make sure you can extract all flavours and the smaller the pieces the greater the flavour potential. See here: https://mesubim.com/2013/12/17/mirepoix-stock/
Keep the lobster aside and chop some onion and fennel and some garlic – sauté and deglaze with some vermouth, or white wine. Then add a tablespoon of flour and you have and mix it well and add some liquid of choice to make sure the flour is well mixed.
Then add the lobster bits and lower the heat and add tomatoes mixed at high-speed in a bimby, or an other mixer. Cook it for 20-minutes and take a bamix and crush all the parts, so you extract all flavours. You can add some anise star, or whatever you feel will add some depth of taste. After thirty minutes of slow cooking you let it cool down completely, and then pass it through a chinois (conical sieve) and you have a lobster bisque.