Be very careful. A partnership is like a marriage, especially if you're working together. You'll spend more time with your partners than you'll spend with your family so you need to know them very well before making a decision. Be sure you have similar goals for the business, a similar work ethic and complimentary skill sets. If what you really need is a sales person or an advertising person, adding another developer won't help much. I'd recommend a trial period to make sure everything is going to work, unless you already know them very well and trust them without question.
The next thing you need is a partnership agreement. Define everything, and I mean everything, that might be an issue. What are the individual roles and responsibilities? How much will each person get paid and how are raises decided? How much vacation time will be allotted per year and is it paid vacation? What happens if one of them gets pregnant or their wife has a child? Do they get time off with or without pay? Who will do their work when they're away? Will you get key-man insurance to pay a salary if one of you gets hit by a bus? How will you handle the profits? Will you reinvest them or pay them out in bonuses or a combination of both? Discussing these issues upfront could save your partnership down the road.
As far as deciding how much percentage to give the partners, I'd suggest trying to determine how much your business is worth today and basing it on that. A quick and dirty way to calculate value is to multiply your annual revenue by 3. That's pretty conservative so you might want to use 5 or more.
You can also estimate the amount of time (in hours) you've spent building the business to this point and multiply that by the amount you would have paid a developer or other contractors to do it. Your goal is to get to your basis in the company: how much you've already put into it out of your own time and money.
Once you determine the current value of the business and your basis in it, you can figure out what percentage partners should get based on the amount of money they want to invest. So if your business is worth 6 lakhs and each partner wants to invest 1 lakh (hopefully I'm using your currency correctly), you may want to offer them a 16% share (1/6). I'm assuming you will all be drawing a salary. If they won't be drawing a salary but you still will, their basis will increase and they'll deserve a higher percentage.
I'd also suggest you require the funds be placed in an escrow account or stated in a promissory note if they're only going to pay monthly. The last thing you want to do is give away some of your company based on a future investment, only to have the money dry up before it's all paid. You'll want to account for this in your partnership agreement, too. What happens if they fail to pay? Do they forfeit their share? Do they have a grace period of a few days or a month? If they default, do you have to pay back the funds they've already invested?
I'm not sure how the tax laws work in India, so I'd also recommend speaking to a tax accountant for advice. In the US, we have specific tax laws around partnerships, ownership and basis.
The best partnerships evolve over time and develop out of a mutual respect for each other and each person brings complimentary skill sets. Most partnerships don't work very well and often end up destroying the business. Make sure you really need them and they'll add value before you agree to anything. If you need the money to grow your business, consider giving them a percentage for their investment only as silent partners and don't work with them.
Hope this helps. Good luck!
JP Stonestreet
www.WebToRich.com
Don't make a living...make a million!