1. Do I need that much money? Maybe you do, but I'd guess that you probably don't need that much yet. Why not accept a smaller amount (for a smaller slice of the company)? In the future, if things work out you could give them an option of investing further.
2. Are you comfortable taking the money and possibly losing it? Odds are that you'll likely fail (sorry, not sure how else to word this) - will it ruin relationships? This isn't an easy question to answer.
If I were in your shoes, I'd probably try to take a small investment from each which will give you the capital to run for 3-6 months. After that, if things are going well (and hopefully they will be) - think bigger.
Disclaimer: I've never taken any investment so feel free to ignore my advice completely.