RESP - Contributing too much? | General financial discussion | Discussion forum

I have 3 kids. Oldest is 11; youngest is 4. There is a decent university in our city. Cost of tuition in todays dollars (for a 4 year degree for each kid) would be around $75 k. It would be a lot higher if they are living away from home, but they don't need to.

Question 1: Should I keep contributing?
I have $110 k in a family RESPs (I've contributed enough to get the maximum match each year). And I still can contribute for quite a number of years. But my question is should I? My concern is what happens if my kids don't use up the funds we set aside? I understand that there is no issue with getting the funds I contribute out of the RESP, but any interest earned on this is taxed at a rate that is 20% higher than my marginal rate. I understand I can transfer $50 k of this interest into an RRSP if I have room with no tax implications. But if I keep contributing to the RESP, it is likely I will have income from my contributions I can't shelter.

Question 2 (this one is dumb): When my kids use the money for education, are they able to select which money they use up? For instance, the RESP will be composed of money I put in, money the government put in, as well as interest on both. So can they pay their tuition first out of the grant money, and then out of the interest earned, and finally out of the money I put in? The reason I ask this question is because it sounds like I can pull the money I put into the RESP at any time with no tax consequences, and I can put the interest earned on my money into an RRSP. So it seems like they treat the source of the money in the RESP different in these cases. So, are we able to be selective in which money we withdraw?