J.N.
Hi. I am the mother of four boys, and had similar problems with my oldest 2 when I was pregnant with my third. Part of the reason for this new behavior might be their uncertainty about your pregnancy and what a new baby means. They probably both are aware that babies have their diapers changed, and may be wanting some of the same attention from you. Here are some suggestions that worked for me.
First I told them how much I loved them and that nothing would ever change that. No matter how big our family became, I could never love them less, or the baby more than them. I also explained that even though babies did take a lot of time and care, I would still find time for them. Then I asked my boys how they felt when their bottoms were so red. Of course, they both said it was uncomfortable, itched and just plain hurt. I asked them why they thought it happened. They said they didn't know (typical, by the way). When I explained that they were not wiping enough, they both said they did wipe. I told them again, not well enough. I reminded them that they were big boys, and I had confidence they could become completely independant in the bathroom, just like daddy. I asked them who felt the discomfort and pain they were experincing on their bottoms. Was it mommy or daddy? Did mommy or daddy hurt when the boys didn't wipe? When they understood that it was their own actions causing the pain, and understood that they needed to wipe until the tissue was clean, they finally started wiping enough. Be sure to praise their efforts as they become better at this task. I would discourage the wet wipes, as not having them at away from home would give them another excuse not to wipe correctly.
With the peeing, boys (as well as men) love to aim at things. Your son might be finding aiming at the bath tub drain a fun activity. In Sweden, they have a fly painted inside the bowl of public toilets, and have found their "splash" rate greatly decreased as the men tried to hit the fly with their pee. (Funny, but true.) Try giving them something to aim at. I used cheerios, but you might think of something even more clever. Just remember, this too will pass, as children do grow up (all too fast, I have learned) and these activities will stop. Hang in there!
A little bit about me. I am the mother of six children, 4 boys, 2 girls with a large age range of 32 to 6. I have been a foster parent for many years, and have had the priviledge of having over 40 children in my home. They have all taught me a great deal and have given my much joy. My six year old was adopted through the foster care system, as she had no relatives who wanted her and was considered too old to adopt by most people searching. She was such a treasure and we already loved her, so we immediately said we would adopt her. She has a lot of fun being an aunt to a niece who is 2 months older than she is. She has a huge family now, and we all love her.