I wouldn't use the same initials for a DS as my DH, as there is a distinct possibility with costs of housing etc that adult children will still live with you. And all post of importance got sent to home while at uni. So 2 Mr D Smiths could well get confused. But Miss or Mrs will distinguish the others. I would try to make sure middle initials were at least different, most official stuff uses them all. Equally it hardly matters, we get so little post other than junk now! So if the name is something you love, it wouldn't put me off really.
My grand parents, parents, brother (and soon to be SIL) and cousin all have the same initial (I don't mean just indivisual the couples - all 7 of them have the single same letter starting their names). Not been a massive problem so far although as they all, except the STBSIL, use the same Drs surgery and pharmacy has occasionally led to some mix ups. Doesn't help that my grandad, dad and brother all have the same name, as does someone not known to us who lives up the road (poor pharmacist )