Welcome to our forum and congratulations on your upcoming arrivals. I am hoping the breeder has your kittens spayed and neutered before you get them. This is a HUGE help in preventing them from marking (females can mark as well). And, if you keep them indoors where "territory" isn't marked by other cats.
Please let up the cat trees now. Bengals love to climb and need that. Trees are easily assembled and easily unassembled.
As for the calming spray and diffuser. I have the Feliway Diffuser in our bedroom because my male bengal (who was neutered at 12 weeks but his previous owner allowed him to roam free outdoors) marks around our bed. This has not completely stopped it, unfortunately! But he does this rarely.
Your kitties will be stressed out simply by leaving their mom. Having siblings, they will be used to each other and each other's smell already, so that shouldn't be an issue. But coming to a new home, with new smells and new people could cause them to be completely stressed out -- and then you move again.
Does anyone know how to move if you have a cat? The BEST way is the clear out one room completely, put the cats and carriers in there with food, water and litter box and nobody opens that door until all exterior doors are closed. Reverse the situation when you move to the new house. Either make the cats the last thing you bring over or put them into a spare room with food, water, litter box and nobody opens that door until the furniture has been moved in and all exterior doors are closed. I can't tell you the number of cats that go missing because "we were moving and she got out the open door." One person even moved the cat with the couch and it was two days before she found the cat after going back to the old home looking for her.
Make sure you have enough litter boxes. You need a minimum of two and preferably three. If your home is especially large or you have multi levels, add more. These little feet have a ways to go to relieve themselves and sometimes they just don't have the bladder control yet. They may have accidents if you overplay with them as well. Remember, they are young and new to all of this, so please have patience and make it easy for them to find a litter box.
You will want a ton of scratching posts. There should be posts on the cat trees, but having extras all around will really help save your furniture. Cats are drawn to any surface that they can scratch. People have been resourceful and added scratchers on the wall for cats. Mine uses cheap scratchers that we get from Walmar but will also use the legs of the trees. He does not scratch our furniture.
Most of all, you need to just enjoy the experience of owning bengals. They are not for the faint of heart and they will not be like any other cat you have ever owned. The members of this forum are wonderful about suggesting and answering questions. We are here if you need our help.
Oh ... and it is mandatory that you post pictures either in Introductions or the Gallery.