I would state it even stronger than Snake!

Never use Excel for anything beyond 1 simple tabel or some small
supporting tables. What you want(referential integrity, keys) can be
simulated/hacked/kludged in Excel. I did it just for fun to see if it
could be done. But I do not condone this for business practice. Pls
learn database moddelling (you seem to know something already) and use
a proper database. Follow Snakes advice, although if money is tight use
a free database(MS has SQL Express, but there are many alternatives out
there).

DM Unseen