Your son will get over his separation anxiety in time. Sometimes you have to limit the time they spend with others, but it's unacceptable that he will not stay with his own father! I don't know what you mean when you say you can't "get him" to stay with your husband. The way to do that is NOT to wait until he stops crying - the way to do it is to give him a quick kiss and hug goodbye, say "Mommy will be back soon" and then leave. Period. Your husband is not his babysitter, he is his father. Child care is not optional. Your child won't learn to stay with anyone if you don't require it. Chances are he will not cry for long - kids that age are famous for fussing for 5 minutes and then getting tired of it. Don't sneak away, but do say goodbye and then leave, and stay gone for a few hours. Do this for a month, then have him stay part of the time with your parents and your husband together. Have your husband leave the room a few times while Grandma and Grandpa keep playing.
Your son should not be in a walker (not good for their legs at all!) or in a play pen (too confining). This is probably why his feet turn in - you've not allowed him to move properly. He should be crawling or walking and using those leg muscles. He will learn to walk on his own - some kids do it at 9 months and some at 14 months, so it's hard to know when is natural for your son. But you won't find out until you let him out to explore and work those muscles.
All kids fall. You are postponing it but you cannot avoid it. Kids have very hard heads and very thick skulls particularly in the front and the back. They don't fall as far as you or I do. They get bumped, they cry sometimes and other times do not, and then they move on. It doesn't matter if you have wood flooring - kids get bumps on carpeting too.
So childproof your house as much as you can - no breakable stuff, nothing important down where he can reach it, put safety guards in the electrical outlets, raise up venetian blind cords beyond his reach, install a gate on the stairs, and put any household chemicals out of reach or behind cabinet locks. You can get corner guards for sharp corners of coffee tables and fireplace hearths. There are safety products available everywhere and these are what all parents use to keep their kids safe and out of playpens. Put his toys and books in a place where he can get to them - a low shelf or a basket or a few storage bins. Let him develop naturally by going from one place to the other to get his things. Let him play on the floor but don't hand him his toys - let him go get them on his own.
Then take him outside and let him crawl around on the grass and learn to start walking. Kids need to get dirty sometimes! They need to play or walk in the sand! They need to dig in the dirt! They need to go on little nature walks and go to the park and go to the petting zoo. All kids learning to walk have a bump on their heads now and then, and they all have bruises on their shins. That's part of life. You cannot protect him from everything, and you will do him a great disservice if you try. When he falls, don't panic. Don't always rush over and make a big deal of it. Half the time, they don't cry anyway. If he does, just say "Whoops, you're okay. Let's try again." Don't fuss excessively. If he's got a little cut, just put a bandaid on it and keep going. (I always kept one or two in my pocket anyway.) But don't put a bandaid on everything - it's not a good lesson in life! Sometimes life knocks you down, you know? So you get up and keep on going!
We all want to protect our kids, so that's natural. And we do make them hold our hands when we cross the street, and we do make them wear seat belts, and we do make them wear helmets when they're riding bikes and scooters. But we cannot always protect them from every little bump or scratch, and we absolutely should not hold them back from exploring or walking or learning because we're afraid. That just creates more frightened children. You'll get better at this when you see that he can go through life, survive and have fun!