No, he can't change the locks if it's in both names.
Respect, if there's no violence in the mix, then you just need to pack for the next few days and your Dad can come and get some more stuff if need be. So grab one big suitcase, if you've got one on wheels, and let's pack assuming that it'll have to be the train. Your son in a stroller, and you can drag the suitcase if you need to, it'll be fine. Also a backpack if you have one. Don't worry about getting this perfect, but here's a list:
Suitcase:
Nappies for a week (but there's presumably shops near your parents, so just pack what you've got).
Bottles/sippy cups/toddler cutlery/plastic bowls or plates, presuming your parents don't have those things.
Stuff as many of your son's clothes in as you possibly can. You know what they're like at that age, and the clothes are small.
Is there somewhere for your son to sleep at your parents? Think about where, and depending on the answer you might want to pack his pillow or blanket or not bother.
Favourite cuddly toy/s, a few books, again depends on how much stuff there is at parents house.
Your clothes: chuck in a lot of knickers and bras, a couple of pairs of jeans and t-shirts, and one good/smart jacket. One skirt and a pair of low heels if that's your style, you never know when you might have to go see CAB or someone and it helps to feel a bit smart.
Toiletries. Tooth stuff for both, hairbrush, any baby shampoo or special stuff you use for DS. Make-up bag.
Backpack:
Books, small toy, snacks. Couple of nappies and wipes. It's your travel bag, pack what you would for a day out plus a couple of activities.
PHONE CHARGER. Sorry to shout but it's important and easily forgotten.
Obviously wallet/keys/etc.
Other things to do: call bank and put a freeze on any joint account. Transfer money to your account as insurance (er, before you do the freeze). Call a friend and tell them what's going on. Put an outgoing message on the answering machine saying "if you want to speak to Respect, please ring her mobile phone". He won't check it.
That's all i can think of.