Your "Grandpa" line will only work for so long if you're bringing in halves week after week. What you need is a dedicated dump bank. See if you can find one bank that will let you dump halves, opening a new account if that's what it takes. Be honest with them and let them know you'll be bringing in coins for deposit on a regular basis, and figure out their comfort level with respect to volume. Build relationships with the tellers and managers, and eventually you'll work it out where everyone's happy.
What I DON'T recommend is overwhelming them. Start slow at first and work your way up in volume. If you're bringing in $500 or $1,000 or more every week and they're not prepared for it, of course you're going to get resistance, and eventually get cut off.
With respect to your specific questions, I'd answer along the following lines:
1. Tell them you collect halves. Never say silver, but tell them you buy rolls "when you can find them" and that you look for old dates, proofs, errors, and coins Not Intended For Circulation. I find that the error line works best - true in my case - particularly if you can go into detail about specific error coins, such as the 1974-D doubled die. The more you sound like a coin nerd and less like a CRH'er, the more tolerant they'll be.
2. Say something like "I'm sorry, I don't mean to be a burden. How many can you take? I get a lot of these but I'll do my best not to inconvenience you." Always be polite and accommodating.
3. When they say they can't accept them, I suspect what they mean is they can't accept that many of them. Again, be honest with them (relatively - there's a difference between the truth and "the truth, the whole truth, and nothing but the truth"), let them know you pick them up where you can find them, sometimes a few coins at a time or rolls when available, and that you generally save them up until you have enough to bring in, but that it sounds like you're bringing in too many at once. Again, if you work at it, you can likely find out how many you can bring in at once without causing them heartache. With 6 accounts, and presumably more than one branch per account, you should be able to spread your dumps so as to not inconvenience any particular bank.
This hobby is pretty much a trial and error process, and is definitely not for the thin-skinned; it took me the better part of a year to figure out the best set up for me, but now I can go through 6 boxes per week with no problem, and could likely do 10 or more if I had the bankroll for it.
Just remember, honey catches a lot more flies than vinegar, and a box of cookies every now and then pays off in the end.
