Adiyen has two Salagrama deities at my home in America donated by my father and father-in-law. It is considered inauspicious to have two deities as one, four or more deities are to be worshipped. I shall try to obtain the required set of deities. But my question is will Perumal harm his devotees for this?

One Salagrama deity is allowed to be worshipped
If there are two Salagrama deities, thirumanjanam and other offerings should be conducted in a grand and elaborate manner for one of the Salagrama deities and they can be kept separately in a box or two different boxes.
Thirumanjanam should be done primarily to one of the deities along with other offerings while all the offerings except thriumanjanam are to be done to the other deity until one obtains two more Salagrama deities.