Hi, My son is now 10 months old and was THE WORST SLEEPER EVER!, so I understand and wanted to share what worked for us.
Basically, once he was good sleeping on his own at night, the naps just followed suit. That didn't happen until last month, though. So, because there is some scientific evidence that letting a little baby "cry it out" isn't good for him, I sucked it up, and rocked and nursed and did whatever, until he was about 6 mos old.
At that age, my son at least suddenly seemed more able to fall asleep and stay asleep and was just a little more developmentally ready to be on his own more.
If your mom-in-law is there to help, I'd take it. If she wants to rock him for his naps, great. Again, for us, the main thing was getting him to go to sleep at night on his own--once he could do that, the ability to nap well just followed.
Whatever you end up doing, just remember that this too shall pass. It's crazy how they get big so fast. You won't believe it but you'll miss the helpless and fussy phase.
Good Luck.