My former spouse has offered to give 1/2 of his 401K to me, only 7,500, because he has run into major financial issues and cannot pay his ordered child support, my concern is that he is transferring the other 1/2 into an IRA, so how much will I have to pay in penalties taxes etc on the 7,500? Will I also be paying (without my knowledge) taxes or transfer fees on the other half that he is moving into an IRA? Any knowledge or input on this would be greatly appreciated! I'm new, hope I've asked this in the correct location :)

Well it depends on how the agreement is worded, but you shouldn't have to pay anything.

Its his decision to cash out the 401(k). Therefore the income will be reported on a 1099 in his name only. He will be responsible for taxes and penalities on the full amount. Whatever he pays you goes towards his arrears in child support.