Very often Silkies or Polish will get mobbed and even killed by normal looking hens that were not raised with them from a young age.
RIR or RIR mixes are known to be racists and rather mercyless in their persuit to keep "strangers" out and away from their premises.
If you are set to get these two new chickens, I would advise to rehome your RIR mix first.
ETA: I just looked at your pictures and judging by the size of this tiny coop it would be best to only house two bantams (Silkies or whatever) in it.
RIR or RIR mixes are known to be racists and rather mercyless in their persuit to keep "strangers" out and away from their premises.
If you are set to get these two new chickens, I would advise to rehome your RIR mix first.
ETA: I just looked at your pictures and judging by the size of this tiny coop it would be best to only house two bantams (Silkies or whatever) in it.