don't know if it is the same problem my husband has or not, but he has had lumps appear and disappear in his armpits as well, it was a collection of puss due to an ingrown hair or something, it stunk to high heaven when getting the thick white pasty stuff out, but healed up quickly and went away, his was red and very sore to start with as well, it was movable and did not seem to be attached to anything, if it is not movable or seems to be attached to something (underlying tissue), you should probably consult a doctor to check for lymph problems, especially since you said they are spreading downward, unless your husband has had major sweating or something, my solution is probably of no help.
as much i research about the lump is there very serious lumps too my husband has it in his arm and back but its not painfull its called lipoma . but you said your husband has painfull one so i would tell see the doctor ASAP . hope this answer help you.
painful lump could be a abscess or a lympn node enlargement.if the abscess is soft and fluctuant it may need a incision to drain the pus.if it is lymph node enlargement it needs evaluation.consult a doctor.