Oh deige I'm so sorry
as a mother all you want to do is protect your children from the things that will hurt them, but that is not always in our hands.
The first thing I worried about when told dd2 had died was how I would tell the children. I was 40+5 weeks pregnant with her so not at all the same as your circumstances but I know that feeling of desperately wanting to do a 'good job' at giving such upsetting news.
You know your children so will be best a judging if telling them seperately or together will help. Seperately allows them to process the information in their own way without influencing someone else's grief, fro example the reaction of a teenager would be very different to a tiny child. However, telling them together, maybe if the older ones were snuggled up with the little ones it might help to keep that oxytocin flowing and make them feel like you are all in this together.
Suicide is an awful thing for a child to get their head around but please try to be as open as you can because the truth is not as scary as the gaps they will fill with their own imaginations.
Try to keep away to likening death to sleep etc because little ones can be very literal and it can make the fearful of sleep.
When my little Azra died we were given books about explaining death to a child from the funeral directors free of charge, they were brilliant, if you are delaying telling them maybe try to pop and get one, or ask someone to do it for you and have a read through first.
In the long term just let them talk through everything, let them see you cry so they know it is ok to be open about their own grief, if they are in the UK schools offer a SEASONS of CHANGE course for children experiencing loss, which are really lovely and delivered normally be someone in the school with special training. It also means they have someone at school who they can open up to and maybe ask questions about their father without wanting to worry you.
Michael Rosen's Sad Book is brilliant too.
All the best and the warmest of hugs to you and your children 