It's really best that you have at least a pair of side surround speakers, but worst case, if you can only have them overhead, I'd probably connect those as Atmos and let the receiver's processor work out the details. It will try to matrix in the effect of anything that's missing. After all...
It’s not possible to have any speakers on the side walls? That‘s really where the first pair of surround speakers should be.
Which receiver did you get?