From my limited knowledge of killis, they are generally at their best in smaller species only tanks. They can be quite shy and not compete well for food. Additionally, rams like warmer water - about 26 - 30 degrees, whereas the killis like it cooler - 21 - 24 degrees. You would have to keep the tank at 25 and no one would be happy! The killis have a short life span anyway and warmer water would speed it up significantly, meaning you may not have them for very long, but the rams would probably not survive long at the lower end of the scale...which would be a shame given how expensive they are to buy!
My advice then would be no. Choose which fish is your 'must have', and build the tank around that fish. If it is your rams then make sure the fish you choose also like soft, warm water.
Have you thought about hatching your own killis in a smaller dedicated tank set up? You can buy eggs from ebay, 20 Australe eggs are about £8 including postage at the moment, they come dried out and you spawn them in peat. Something I have always wanted to try!
A safer option may be something like harlequins, they will stand out against the tetras and rams and you could have a big group.
Have you thought about bottom dwellers? In my 240 i have both peppered corydoras and botia histrionica (loaches), and a couple of plecs. All peaceful but lively and with the rainbowfish, tetra and harlequins it really makes for a stunning display. Cories won't appreciate the high temperatures so they are out but loaches might be a good choice and there is a plec to suit every tank!
