Hi,
I am also a mother in a blended family with four kids. I have two biological (9 and 11), my husband has one adopted (13) and one biological (9). All of us live together, our ex-partners are not involved much. We have been together as a family for 6 years now. People say being a mom, even a single mom is hard, try being a step mother!
We posted a dry erase board on our refrigerator for chores. Each kid has "morning chores" which consist of making their bed, getting dressed and fixing their breakfast.
Then there are "dinner chores" which consist of each kid doing an age appropriate job like sweeping under the table, or feeding the dog, etc.
There are "bedtime chores" in which each kid gets pajamas on, flosses and brushes, and gets ready for our family story time.
And each kid has a weekend chore as well.. these are bigger chores that are only once a week, such as emptying the trash cans in to the main one..
The chart shows the chores (when they were younger it was pictures, now it's words) so each kid can look at it to remind themselves what needs to be done.
On the chart each kid has a "bank account" where they can save up to go "buying". We give each kid $2. allowance per week, 1/2 of their bday and holiday money goes into this spending account and 1/2 goes into a real savings account. We go buying every few months which teaches the kids to budget/save and I believe teaches good work ethics.
The chart also shows a -$.25 when a kid didn't do a chore on time or needed to be reminded. We not only take off money for not doing the chore, we give out an "extra chore" (they took our energy to remind them, they give it back by doing another chore for free).
The cool thing is on the chart there is a list of extra chores that the kids can do to make extra money whenever they feel motivated (which believe it or not happens quite often.
Each week we sit as a family and have a "pay day". Each kid learns a bit of math (how much allowance, then add or subtract and add to the existing account). Usually with each kid theres one chore that is consistently forgotten so they can reflect and do better the next week.
This chart has worked well in our family because the consequence is there, I'm not nagging and reminding to get chores done. Each kid knows ahead of time what is expected so there's not a lot of loop holes or arguing. It's pretty black and white. The kids like this chart as well, they can always look to see how much money they have and dream about what they'd like to spend it on.
When we choose this method, we tried to make it so it wasn't another chore for my husband and I. We sat with the kids as a family and discussed how everyone who lived here needed to help out, that we are a family. We also had a list prepared of age appropriate chores and let the kids pick so they could feel like they were truly working together as a family.
As far as the pooping thing, our 13 year old still wets the bed. He obviously doesn't like it and doesn't want to do it. Even though he's my "stepson" (I actually never call him my step son, to me he's my son), I have made doctor appointments, chiropractor appointments, have done the alarm clock, etc, etc. It's definitely hard for a parent to say my kid has a problem. I explained to my husband at an appropriate time, that I made a doctors appointment for our son to see if there's anything we can do to help him, now that he's 13. My husband was happy to see my involvement, said great let me know how it goes, and my son was happy to feel like someone was trying to help him. Unfortunately, nothing has helped him to stop wetting, yet it did rule out any physical concerns.
As far as discipline, I wouldn't get chores and discipline on the same page or chart if you will. It also must be extremely hard only having some of the kids some of the time. By the time they transition, it's time for them to leave. I'm not good at advise, I can only story tell my experience, however I might think about disciplining the group that's with you all the time and letting the part timers slack a bit. Be more of a friend then a parent to steps, they seem to respect it more.
Let me know if I can share any other stories with you, all in all I feel like my family is hard work and a great reward...
Good Luck