They should come as a seal and a bead for each window. There is a proper tool for putting the bead in,it opens the seal iut and pushes the bead into the recess as you push it along,this pushes the seal out into a snug fit but I have done it with a screwdriver. If you use a screwdriver, be very carefully as its easy to cut the seal, it will also take twice as long.
As for the join, cut the seal slightly longer than needed and then with the two ends facing each other,"make them" fit, this will ensure the two ends are pushing snugly against each other thereby making a good seal.
Have the join for the seal on one side and the join of the bead on the other to give strength and good seal. If you do cut the seal a little short, I'm sure a bit of silicone sealant or dum dum
will do the trick!
Hth , Rob
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