I think you need to get some structure to your days - I always foudn days when I knew what I was going to do much easier.
Firstly, find out about all the baby and toddler groups in your area - library, church, soft play - google Peterborough play groups or similar. Also, Netmums is good for local info like this (better than MN local I think).
Then - all the parks and playgrounds you can get to.
Try to have something on every morning and afternoon. If there's nothing on, plan something for inside the house - have a duplo morning, or painting - that kind of thing. DD used to love painting and then messing around for ages (longer than she spent painting!) 'washing up' - yes, the kitchen floor got all wet but it kept her occupied for a good half hour.
I used to make everyday thinks an outing, like going to the supermaket - that would be a morning activity.
It takes 3 trains and around 90 mins to get to my mum's but I do it every fortnight or so - the journey is exciting for DD, took a backpack filled with books, little toys and snacks. My mum has a lot of toys acquired from other grandmas and charity shops and things on offer in Lidl - could you and your mum build up a small selection to keep at her house?
these are all just suggestions and not all will work for you, or with 2 children (I just have DD), but hopefully something in there might help!
Oh and reward charts - you say they didn't work with potty training, but that might just be because he's not ready to be potty training, so they may work for other things? Or the pasta jar - have a small jam jar and every time he keeps one of the 'rules' (sitting down at lunchtime, not chasing the dog - whatever you want) you put a piece of pasta in - when it's full he gets a treat (not a material treat necessarily, but a trip to his favourite park or something like that). Don't take pasta away for being 'naughty'.
It's hard with little ones, isn't it?!!