I trained Theo with the leash and harness when he was a baby so he would be ok with it when he got older. He chewed the thing like CRAZY so I had to use a spray bottle and spray him with water every time he chewed it. The spray bottle trick worked and now he is fine with the leash and harness. I don't take him outside anymore since he hasn't be vaccinated for RHDV2, but I put the harness on him regularly to keep him used to it.
Keep in mind when taking the rabbit outside on the leash the rabbit is walking you. You only have the leash to keep the rabbit from danger. It will be very hard to walk 2 rabbits at once. You will need to have someone else hold the leash to one of the rabbits. When I used to take Theo out he would drag me underneath bushes and would take off at a full sprit with me being dragged behind him. Also, keep in mind that rabbits can slip out of the harnesses. I had a friend holding Theo's leash and he went under a bush, she pulled the leash and the harness slipped right over Theo's head. I was right there and was able to grab him before he took off running but it could have been dangerous. I
highly suggest getting a playpen for your rabbits because it is easier to take them outside if you have a playpen.
I believe your rabbits are only 8 weeks? If so, they should not be getting veggies yet so you should slowly remove them from their diet. Once they turn 3 months you can very slowly introduce veggies to their diet. Start out giving them 1 tbs of one type of veggie per day to prevent them from getting
Gi Stasis, you can add to that amount if there is no change in their poops (watery poops/weird-shaped poops would be a sign that you gave them too many veggies). I think that is bok choy on the plate which is ok in small amounts for an adult rabbit but can very likely cause gas which can cause Gi Stasis.