Songshare agreements are pretty simple documents. Pretty much as are being described here.
Just be aware any contract you make, if a major wanted to fck you over, their lawyers could absolutely discredit your contracts. They're levels above even any lawyer you could probably afford.
Just get decent reasonable contracts written up. If you have zero understanding, then best to get a lawyer to draft some. And even if you do know, to get a lawyer to check 'em, just give 'em the go ahead.
The contract you MORE want to concern yourself with getting a lawyer, is if you sign a deal with management, publishing, record label... etc. Those ones you WILL want to get a music lawyer to look at, because you likely won't have any real clue what you're looking at, even if you understand it you might not have any real bearing on what is reasonable and unreasonable in a contract.
You really don't need a lawyer to do a simple songshare agreement.