The clowns are probably going to fight with or without any Anemone as they age. (Tomato will probably come out on top)
There is really no reason at all to purchase an Anemone for the clowns in the first place. The clowns will do fine without but I would look at removing one or the other and perhaps getting a mate for the one you keep.
I suppose the 2 of the could get along but in time I think the odds are against you. If the tank was say 2X larger, you would stand a better chance I think.
Lastly, keeping 1 Anemone alive for any period of time is typically a pretty good accomplishment.
Keeping 2 of them alive (that are not clones) might be considered either really good or just lucky.
Unless your tank is at least a year old and extremely stable, the only thing you are going to do is kill the Anemone (they live to be over 100+ in the wild.
If you think you can pull it off, I would suggest captive raised E.Quadricolor as they are among the hardiest and easiest to keep (read: they are hard to keep and pretty fragile, however when it comes to Anemone's, they are your best bet besides a Condylactus) There are literally days worth of reading on Anemone's so you should be able to go forward with your eyes open with a bit of effort.