I'm sorry to hear your partner isn't well and is in hospital, that's a stressful thing for anyone. I hope he feels better soon, @ThankYouMama .
It sounds to me like you and your family really need some extra support and you need help with your own mental health - it's a huge strain, having to juggle everything while managing your own issues.
Firstly, could you get nanny or childminder or nursery help with your youngest, rather than them having to be sent elsewhere for care? At 17 months, their attachment to their primary caregivers is so important - boy or girl, they need to be with you if you're at all able to do that.
Secondly, your older son is old enough to be picking up that dad gone away and their baby sibling has gone away, and to be distressed and feel insecure because of this. He needs to see that people may go away, but they come back - bring his sibling back home. He also needs consistent routines, structure and boundaries. He doesn't need trips to toy shops. He needs to know he's safe and secure.
Thirdly, I think there are several things in how you and your partner have been coping with his OCD and your anxiety that are potentially not good longer term for your children. Obsessively checking for bruising and expressing fears about the people around them are just going to create those fears for your children - what they need is to see mum and dad containing and managing anxieties, responding to concerns in proportionate ways, and helping them feel safe and secure with others. I think you both might benefit from some help with this.
Finally, it sounds like you have some ongoing disappointment at having a second son, especially as it's influencing how you treat him. You need to address this otherwise he will pick up on it and it will harm him.